For the relations of Artaxerxes I.—III. with the Jews seeJews, §§ 19-21. For bibliographical references seePersia:Ancient History.The name Artaxerxes was adopted by Bessus when he proclaimed himself king after the assassination of Darius III. It was borne by several dynasts of Persis, when it formed an independent kingdom in the time of the Parthian empire (on their coins they call themselves Artakhshathr; one of them is mentioned by Lucian,Macrobii, 15), and by three kings of the Sassanid dynasty, who are better known under the modern form Ardashir (q.v.).
For the relations of Artaxerxes I.—III. with the Jews seeJews, §§ 19-21. For bibliographical references seePersia:Ancient History.
The name Artaxerxes was adopted by Bessus when he proclaimed himself king after the assassination of Darius III. It was borne by several dynasts of Persis, when it formed an independent kingdom in the time of the Parthian empire (on their coins they call themselves Artakhshathr; one of them is mentioned by Lucian,Macrobii, 15), and by three kings of the Sassanid dynasty, who are better known under the modern form Ardashir (q.v.).
(Ed. M.)
ARTEDI, PETER(1705-1735), Swedish naturalist, was born in the province of Angermania, in Sweden, on the 22nd of February 1705. Intending to become a clergyman, he went, in 1724, to study theology at Upsala, but he turned his attention to medicine and natural history, especially ichthyology, upon the study of which he exercised great influence (seeIchthyology). In 1728 his countryman Linnaeus arrived in Upsala, and a lasting friendship was formed between the two. In 1732 both left Upsala, Artedi for England, and Linnaeus for Lapland; but before parting they reciprocally bequeathed to each other their manuscripts and books in the event of death. He was accidentally drowned on the 27th of September 1735 at Amsterdam, where he was engaged in cataloguing the collections of Albert Seba, a wealthy Dutchman, who had formed what was perhaps the richest museum of his time. According to agreement, his manuscripts came into the hands of Linnaeus, and hisBibliotheca IchthyologicaandPhilosophia Ichthyologica, together with a life of the author, were published at Leiden in the year 1738.
ARTEGA,a tribe of African “Arabs,” said to be descendants of a sheik of that name who came from Hadramut in pre-Islamic days, settling near Tokar. The name is said to be “patrician,” and the Artega may be regarded as the most ancient stock in the Suakin district. They are now an inferior mixed race. They were all followers of the mahdi and khalifa in the Sudan wars (1883-1898).
SeeAnglo-Egyptian Sudan, edited by Count Gleichen (London, 1905).
SeeAnglo-Egyptian Sudan, edited by Count Gleichen (London, 1905).
ARTEL(Russ. for “gang”), the name for the co-operative associations in Russia. Originally, the artels were true examples of productive co-operation, bodies of working-men associating together for the purpose of jointly undertaking some piece of work, and dividing the profits. This original form of artel still survives among the fishermen of Archangel. Artels have come, however, to be little more than trade gilds, with mutual responsibility. (For details seeRussia.)
ARTEMIDORUS. (1) A geographer “of Ephesus” who flourished about 100B.C.After studying at Alexandria, he travelled extensively and published the results of his investigations in a large work on general geography (Τὰ γεωγραφούμενα) in eleven books, much used by Strabo and others. The original work is lost, but we possess many small fragments and larger fragments of an abridgment made by Marcianus of Heracleia (5th century), which contains the periplus of the Euxine and accounts of Bithynia and Paphlagonia. (See Müller,Geographi Graeci Minores; Bunbury,History of Ancient Geography; Stiehle, “Der Geograph Artemidoros von Ephesos,” inPhilologus, xi., 1856). (2) A soothsayer and interpreter of dreams, who flourished in the 2nd centuryA.D., during the reigns of Hadrian and the Antonines. He called himself Daldianus from his mother’s birthplace, Daldis in Lydia, in order to make its name known to the world. HisὈνειροκριτικά, or interpretation of dreams, was said to have been written by command of Apollo Daldianus, whose initiated votary he was. It is in four books, with an appendix containing a collection of prophetic dreams which had been realized. The first three books, addressed to Cassius Maximus, a Phoenician rhetorician (perhaps identical with Maximus of Tyre), treat of dreams and divination generally; the fourth—with a reply to his critics—and the appendix are dedicated to his son, also named Artemidorus and an interpreter of dreams. Artemidorus boasts of the trouble expended on his work; he had read all the authorities on dreams, travelled extensively, and conversed with all who had studied the subject. The work is valuable as affording an insight into ancient superstitions. According to Suidas, Artemidorus also wrote on augurs and cheiromancy, but all trace of these works is lost. (Editions: Reiff, 1805, Hercher, 1864; translation and notes, Krauss, 1881; English translation by Wood, 1644, and later editions.)
ARTEMIS,one of the principal goddesses in Greek mythology, the counterpart of the Roman Diana. The suggested etymologies of the name (see O. Gruppe,Griechische Mythologie, ii. p. 1267, note 2), as in the case of most of the Olympian deities, are unsatisfactory, and throw no light upon her significance and characteristics. The Homeric and later conception of Artemis, though by no means the original one, may be noticed first. She is the daughter of Zeus and Leto, twin-sister and counterpart of Apollo. She is said to have been born a day before him (on the 6th of the month) and tradition assigns them different birthplaces—Delos to Apollo, Ortygia to Artemis. But Ortygia (“home of quails”) applies still to Delos, and may well have been a synonym for that island. In its original sense it does not apply either to the island of Ortygia at Syracuse, or to Ortygia near Ephesus, which also claimed the honour of having been the birthplace of the goddess. Artemis is the goddess of chastity, an aspect of her character which gradually assumed more and more importance—the protectress of young men and maidens, who defies and contemns the power of Aphrodite. Her resemblance to her brother is shown in many ways. Like him, armed with bow and arrows, she deals death to mortals, sometimes gently and suddenly, especially to women, but also as a punishment for offences against herself or morality. With him she takes part in the combat with Python and with Tityus, in the slaughter of the children of Niobe, while alone she executes vengeance on Orion. Although Apollo has nothing to do with the earlier cult of Artemis, nor Artemis with that of Delphi, their association was a comparatively early one, and probably originated in Delos. Here the connexion of Artemis with the Hyperborean legend (seeApollo) is shown in the names of the maidens (Opis, Hecaerge) who were supposed to have brought offerings from the north to Delos, where they were buried. Both Opis (or Oupis) and Hecaerge are names of Artemis, the latter being the feminine of Hecaergos, an epithet of Apollo. Like her brother, she is notonly a goddess who deals death, but she is also a healing and a purifying divinity,οὐλία(“the healer,” cf. Apollo Oulios),λύη, λυαία(“purifier,”) andσώτειρα, “she who saves from all evils” (cf. Apolloἀποτρόπαιος). Her connexion with the prophetic art is doubtful, although mention is made of an Artemis Sibylla. To her association with Apollo are certainly to be referred the names Delphinia and Pythia, and the titles referring to state and family life—προστατηρία,πατριῶτις,βουλαία. It probably accounts for her appearance as a goddess of seafarers, the bestower of fair weather and prosperous voyages. At Phigalia in Arcadia, Eurynome, represented as half woman and half fish, was probably another form of Artemis. To the same association may be traced her slight connexion with music, song and dance.
It is in the Arcadian and Athenian rites and legends, however, which are certainly earlier than Homer, that the original conception of the goddess is to be found. These tend to show that Artemis was first and foremost a nature goddess, whose cult shows numerous traces of totemism. As a goddess of fertilizing moisture, lakes, rivers, springs, and marshy lowlands are brought into close connexion with her. Thus she isλιμναία, δέσποινα λίμνης(“lady of the lake”),ἑλεία(“of marshes”),ποταμία(“of rivers,” especially of the Cladaus and Alpheus, whence her nameἈλφειαία). Her influence is very active in promoting the increase of the fruits of the field, hence she is specially a goddess of agriculture. She drives away the mice (cf. Apollo Smintheus) and slays the Aloidae, the corn spirits; she is the friend of the reapers, and requires her share of the first fruits. Her character as a harvest goddess is clearly shown in the legend of the Calydonian boar, sent by her to ravage the fields out of resentment at not having received a harvest offering from Oeneus (seeMeleager). Asἐπιμύλιοςandἐπικλιβάνιος(“presiding over the mill and the oven”) she extends her protection over the further development of the grain for the use of man.
Artemis was naturally also a goddess of trees and vegetation. Near Orchomenus her wooden image stood in a large cedar-tree—an indication that her worship was originally that of the tree itself (κεδρεᾶτις, “the cedar goddess”); at Caryae there was an image of Artemisκαρυᾶτις(“the nut-tree goddess”). Two curious epithets in this connexion deserve notice:λυγοδέσμα(“bound with withies”), derived from the legend that the image of Artemis Orthia was found in a thicket of withies, which twined round it and kept it upright (λύγοςis theagnus castus, and points to Artemis in her relation to women); andἀπαγχομένη(“the suspended”), probably a reference to the custom of hanging the mask or image of a vegetation-divinity on a tree to obtain fertility (Farnell,Cults of the Greek States, ii. p. 429; cf. the “swing” festival (αἰώρα) of the Greeks, and theoscillaof the Romans).
The functions of the goddess extended from the vegetable to the animal world, to the inhabitants of the woods and mountains. This is clearly expressed in the cult of Artemis Laphria (possibly connected withλάφυρα, “spoils”), at whose festivals all kinds of animals, both wild and tame, as well as fruits, were thrown together on a huge wood fire. Her general name in this connexion wasἀγροτέρα(“roaming the wilds,” not necessarily “goddess of the chase,” an aspect less familiar in the older religion), to whom five hundred goats were offered every year by the Athenians as a thanksgiving in commemoration of the victory at Marathon. Numerous animals were sacred to her, and at Syracuse all kinds of wild beasts, including a lioness, were carried in procession in her honour. It has been observed that she is rather the patroness of the wild beasts of the field than of the more agricultural or domestic animals (Farnell,Cults, ii. p. 431), although the epithetἡμερασία(“the tamer,” according to others, the “gentle” goddess of healing) seems to refer to her connexion with the latter. The bear was especially associated with her in Arcadia, and in her worship as Artemis Brauronia at Brauron in Attica. According to the legend, Callisto, an Arcadian nymph, became by Zeus the mother of Arcas, the eponymous hero of the Arcadians. Zeus, to conceal the amour, changed Callisto into a she-bear; Hera, however, discovered it, and persuaded Artemis to slay Callisto, who was placed amongst the stars asἄρκτος(“the bear”). There is no doubt that Callisto is identical with Artemis; her name is an obvious variation ofκαλλίστη, a frequent epithet of the goddess, to whom a temple was erected on the hill where Callisto was supposed to be buried. It is suggested by M. Kraus inClassical Review, February 1908, that Aphaea, the cult-name of Artemis at Aegina, is of Semitic origin and means “beautiful.” Closely connected with this legend is the worship of Artemis Brauronia. The accounts of its institution, which differ in detail, agree that it was intended to appease the wrath of the goddess at the killing of a bear. A number of young girls, between five and ten years of age, wearing a bear-skin (afterwards a saffron-coloured robe) danced a bear-dance, calledἀρκτεία, the girls themselves being calledἄρκτοι. In one account, a maiden was ordered to be sacrificed to the bear Artemis, but a certain man who had a goat called it his daughter and offered it up in secret, just as at Munychium a fawn dressed up as a girl was sacrificed to the goddess. In place of the goat or fawn a bear might have been expected, but the choice may have been influenced by the animal totem of the tribe into whose hands the ritual fell. The whole is a reminiscence of earlier times, when the goddess herself was a bear, to whom human sacrifice was offered. Callisto was originally a bear-goddess worshipped in Arcadia, identified with Artemis, when nothing remained of the original animal-worship but name and ritual. The worship of Callisto being merged in that of the greater divinity, she became the handmaid and companion of Artemis. A stone figure of a bear found on the Acropolis seems to point to the worship of Artemis Brauronia. Her death at the hands of the latter was explained by the wrath of the goddess—in her later aspect as goddess of chastity—at Callisto’s amour with Zeus (see A. Lang,Myth, Ritual and Religion, ii.; Farnell,Cults, ii. p. 437). The custom of flogging youths at the altar of Artemis Orthia1at Limnaeum in Laconia, and the legend of Iphigeneia (q.v.), herself another form of Artemis, connected with Artemis Taurica of the Tauric Chersonese, are usually supposed to point to early human sacrifice (but see Farnell). Various explanations have been given of the epithetὀρθία: (1) that it refers to the primitive type of the “erect” wooden idol; (2) that it means “she who safely rears children after birth,” or “heals the sick” (cf.ὄρθιοςapplied to Asclepius); (3) that it has a phallic significance (Schreiber in Roscher’sLexikon). Scholars differ as to whether Artemis Taurica is identical with Artemis Tauropolos, worshipped chiefly at Samos with a milder ritual, but it is more probable thatταυροπόλοςsimply means “protectress of bulls.”
The protecting influence of Artemis was extended, like that of Apollo, to the highest animal, man. She was especially concerned in the bringing up of the young. Boys were brought by their nurses to the temple of Artemisκορυθαλία(=κουροτρόφος) and there consecrated to her; at the Apaturia, on the day calledκουρεῶτις, boys cut off and dedicated their hair to her. Girls as well as boys were under her protection. Her function as a goddess of marriage is less certain, and the cult-titles adduced in support of it are hardly convincing; such areἡγεμόνη, interpreted as “she who leads home the bride,”σελασφόρος, “bearer of light,” that is, of torches at the marriage procession. On the other hand, her connexion with childbirth is clearly shown: in many places she is even called Eilithyia, who in the earlier poets was regarded as distinct from her. In one version of the story of her birth she is said to have been born a day before Apollo, in order to assist Leto at his birth; women in childbirth invoked her aid, and after delivery offered up their clothes or a lock of hair. As already noticed, in Homer Artemis appears as a goddess of death; closely akin to this is the conception of her as a goddess of war. As such she isνικηφόρος(“bringer of victory”); the titleκολαινίςis possibly connected withκολεὀς(“sword-sheath”); andλαφρία(see above) may refer to the spoils of war as well as the chase.
The idea of Artemis as a virgin goddess, the “queen and huntress, chaste and fair,” which obtained great prominence in early times, and seems inconsistent with her association with childbirth, is generally explained as due to her connexion with Apollo, but it is suggested by Farnell thatπαρθένοςoriginally meant “unmarried,” and that “Ἄρτεμις παρθένοςmay have been originally the goddess of a people who had not yet the advanced Hellenic institutions of settled marriage ... and when society developed the later family system the goddess remained celibate, though not opposed to childbirth.”
Another view of the original character of Artemis, which has found much support in modern times, is that she was a moon-goddess. But there is no trace of Artemis as such in the epic period, and the Homeric hymn knows nothing of her identification with Selene. The attribute of the torch will apply equally well to the goddess of the chase, and epithets such asφωσφόρος, σελασφόρος, αἰθοπία, although applicable, are by no means convincing. The idea dates from the 5th century, and was due to her connexion with Hecate and Apollo. When the latter came to be identified by philosophical speculation with the sun-god Helios, it was natural that his sister and counterpart should be identified with the moon-goddess Selene. But she is nowhere recognized in cult as such (see Gruppe,Griechische Mythologie, ii. p. 1297, note 2).
It has been mentioned that Callisto, Iphigeneia, Eilithyia, are only Artemis under different names; to these may be added Adrasteia, Atalanta, Helen, Leto and others (see Wernicke in Pauly-Wissowa’sRealencyclopädie).
Again, various non-Hellenic divinities were identified with Artemis, and their cult gradually amalgamated with hers. The most important of these was Artemis of Ephesus, whose seat was in the marshy valley of the Caystrus. Like the Greek Artemis, she was essentially a nature goddess, the great foster-mother of the vegetable and animal kingdom. A number of officials were engaged in the performance of her temple service. Her eunuch priests,μεγάβυζοι(a name which points to a Persian origin), were under the control of a high priest called Essen (according to others, there was a body of priests called Essenes). There were also three classes of priestesses, Mellierae, Hierae, Parierae; there is no evidence that they were called Melissae (“bees”), although the bee is a frequent symbol on the coins of the city. Her chief festival, Ephesia or Artemisia, was held in the spring, at which games and various contests took place after the Greek fashion, although the ritual continued to be of a modified oriental, orgiastic type. This goddess is closely connected with the Amazons (q.v.), who are said to have built her temple and set up her image in the trunk of a tree. The Greeks of Ephesus identified her with their own Artemis, and claimed that her birthplace Ortygia was near Ephesus, not in Delos. She has much in common with the oriental prototype of Aphrodite, and the Cappadocian goddess Ma, another form of Cybele. The usual figure of the Ephesian Artemis, which was said in the first instance to have fallen from heaven, is in the form of a female with many breasts, the symbol of productivity or a token of her function as the all-nourishing mother. From the waist to the feet her image resembles a pillar, narrowing downwards and sculptured all round with rows of animals (lions, rams and bulls).
Mention may also be made of the following non-Hellenic representatives of Artemis. Leucophryne (or Leucophrys), whose worship was brought by emigrants from Magnesia in Thessaly to Magnesia on the Maeander, was a nature goddess, and her representation on coins exactly resembles that of the Ephesian Artemis. Her cult, however, from the little that is known of it appears to have been more Hellenic. There was an altar and temple of Artemis Pergaea at Perga in Pamphylia, where a yearly festival was held in her honour. As in the case of Cybele, mendicant priests were attached to her service. Similar figures were Artemis Coloēnē, worshipped at Lake Coloē near Sardis; Artemis Cordax, celebrated in wanton dances on Mount Sipylus; the Persian Artemis, identical with Anaitis Bendis, was a Thracian goddess of war and the chase, whose cult was introduced into Attica in the middle of the 5th centuryB.C.by Thracian metics. At her festival called Bendidea, held at the Peiraeus, there was a procession of Thracians who were settled in the district, and a torch-race on horseback. (For Britomartis see separate article.)
Among the chief attributes of Artemis are: the hind, specially regarded as her sacred animal; the bear, the boar and the goat; the zebu (Artemis Leucophrys); the lion, one of her oldest animal symbols; bow and arrows, as goddess of the chase and death; a mural crown, as the protectress of cities; the torch, originally an attribute of the goddess of the chase or marriage, but, like the crescent (originally an attribute of the Asiatic nature goddesses), transferred to Artemis, when she came to be regarded as a moon-goddess. The Greek Artemis was usually represented as a huntress with bow and quiver, or torch in her hand, in face very like Apollo, her drapery flowing to her feet, or, more frequently, girt high for speed. She is accompanied often by a deer or a dog. Perhaps the finest existing statue of her is the Diana of Versailles from Hadrian’s Villa (now in the Louvre), in which she wears a short tunic drawn in at the waist and sandals on her feet; her hair is bound up into a knot at the back of her head, with a band over the forehead. With her left hand she holds a stag, while drawing an arrow from the quiver on her shoulder with the right. Another famous statue is one from Gabii, in which she is finishing her toilet and fastening the chlamys over her tunic. In older times her figure is fuller and stronger, and the clothing more complete; certain statues discovered at Delos, imitated from wooden models (xoana), are supposed to represent Artemis; they are described as stiff and rigid, the limbs as it were glued to the body without life or movement, garments closely fitting, the folds of which fall in symmetrical parallel lines. As a goddess of the moon she wears a long robe, carries a torch, and her head is surmounted by a crescent. On the coins of Arcadia, Aetolia, Crete and Sicily, are to be seen varied and beautiful representations of her head as conceived by the Greek artists in the best times.
Authorities.—Articles in Pauly-Wissowa’sRealencyclopädie; Roscher’sLexikon der Mythologie, and Daremberg and Saglio’sDictionnaire des antiquités(s.v. Diana, with well-arranged bibliography); L. Preller,Griechische Mythologie(4th ed. by C. Robert); L.R. Farnell,The Cults of the Greek States, ii. (1896); O. Gruppe,Griechische Mythologie und Religions-Geschichte, ii. (1906); A. Claus,De Dianae antiquissima apud Graecos natura(Breslau, 1880). In the articleGreek Art, fig. 11 (a gold ornament from Camirus) represents the Oriental goddess identified by the Greeks with Artemis.For the Roman goddess identified with Artemis seeDiana.
Authorities.—Articles in Pauly-Wissowa’sRealencyclopädie; Roscher’sLexikon der Mythologie, and Daremberg and Saglio’sDictionnaire des antiquités(s.v. Diana, with well-arranged bibliography); L. Preller,Griechische Mythologie(4th ed. by C. Robert); L.R. Farnell,The Cults of the Greek States, ii. (1896); O. Gruppe,Griechische Mythologie und Religions-Geschichte, ii. (1906); A. Claus,De Dianae antiquissima apud Graecos natura(Breslau, 1880). In the articleGreek Art, fig. 11 (a gold ornament from Camirus) represents the Oriental goddess identified by the Greeks with Artemis.
For the Roman goddess identified with Artemis seeDiana.
(J. H. F.)
1The site of the temple of Artemis Orthia was excavated by the British School of Archaeology at Athens (seeAnnual, 1906). The flogging (διαμαστίγωσις) is explained by R.C. Bosanquet as a late institution of decadent Sparta, an exaggeration of an old ritual practice of whipping away boys who tried to steal cheeses from the altar (seeThe Year’s Work in Classical Studies, ed. W.H.D. Rouse, 1907).
1The site of the temple of Artemis Orthia was excavated by the British School of Archaeology at Athens (seeAnnual, 1906). The flogging (διαμαστίγωσις) is explained by R.C. Bosanquet as a late institution of decadent Sparta, an exaggeration of an old ritual practice of whipping away boys who tried to steal cheeses from the altar (seeThe Year’s Work in Classical Studies, ed. W.H.D. Rouse, 1907).
ARTEMISIA,daughter of Lygdamis, was queen of Halicarnassus and Cos about 480B.C.Being a dependent of Persia, she took part in person in the expedition of Xerxes against the Greeks, and fitted out five ships, with which she distinguished herself in the sea-fight near Salamis (480). When closely pursued by the Athenians she escaped by the stratagem of attacking one of the Persian vessels, whereupon the Athenians concluded that she was an ally, and gave up the pursuit (Herod. vii. 99, viii. 68). After the battle Xerxes declared that the men had fought like women, and the women like men. By her advice he did not risk another battle, but at once retired from Greece. She is said to have loved a young man named Dardanus, of Abydos, and, enraged at his neglect of her, to have put out his eyes while he was asleep. The gods, as a punishment for this, ordered her, by an oracle, to take the famous but rather mythicallover’s leapfrom the Leucadian promontory (Photius,Cod.153a).
ARTEMISIA,the sister and wife of Mausolus (or Maussollus), king of Caria, was sole ruler from about 353 to 350B.C.She has immortalized herself by the honours paid to the memory of her husband. She built for him, in Halicarnassus, a very magnificent tomb, called the Mausoleum, which was one of the seven wonders of the world, and from which the name mausoleum was afterwards given to all tombs remarkable for their grandeur. She appointed panegyrics to be composed in his honour, and offered valuable prizes for the best oratorical and tragic compositions. She alsoerected a monument, or trophy, in Rhodes, to commemorate her conquest of that island. When the Rhodians regained their freedom they built round this trophy so as to render it inaccessible, whence it was known as theAbaton. There are statues of Mausolus and Artemisia in the British Museum.
Vitruvius ii. 8; Diodorus Siculus xvi. 36; Cicero,Tusc.iii. 31; Val. Max. iv. 6.
Vitruvius ii. 8; Diodorus Siculus xvi. 36; Cicero,Tusc.iii. 31; Val. Max. iv. 6.
ARTEMON(fl.c.A.D.230), a prominent Christian teacher at Rome, who held Adoptianist (seeAdoptianism), or humanitarian views, of the same type as his elder contemporaries the Theodotians, though perhaps asserting more definitely than they the superiority of Christ to the prophets in respect of His supernatural birth and sinlessness. He was excommunicated by Zephyrinus, despite his remarkable claim that all that bishop’s predecessors in the see of Rome had held the humanitarian position. (See alsoMonarchianism.)
ARTENA,a village of Italy, in the province of Rome, situated at the N.N.W. extremity of the Volscian Mountains; it is 36 m. S.E. by rail, and 24 m. direct from Rome. Pop. (1901) 5016. On the mountain above it (2073 ft.) are the fine remains of the fortifications of a city built in a very primitive style, in cyclopean blocks of local limestone; within the walls are traces of buildings, and a massive terrace which supported some edifice of importance. The name of this city is quite uncertain; Ecetra is a possible suggestion. The modern village, which was called Monte Fortino until 1870, owes its present name to an unwarrantable identification of the site with the ancient Volscian Artena, destroyed in 404B.C.Another Artena, which belonged to the district of Caere, and lay between it and Veii, was destroyed in the period of the kings, and its site is quite unknown.
See T. Ashby and G.J. Pfeiffer inSupplementary Papers of the American School in Rome, i. 87 seq.
See T. Ashby and G.J. Pfeiffer inSupplementary Papers of the American School in Rome, i. 87 seq.
ARTERIES(Gr.ἀρτηρία, probably fromαἴρειν, to raise, but popularly connected by the ancients withἀήρ, air), in anatomy, the elastic tubes which carry the blood away from the heart to the tissues. As, after death, they are always found empty, the older anatomists believed that they contained air, and to this belief they owe the name, which was originally given to the windpipe (trachea). Two great trunks, the aorta and pulmonary artery, leave the heart and divide again and again, until they become minute vessels to which the name of arterioles is given. The larger trunks are fairly constant in position and receive definite names, but as the smaller branches are reached there is an increasing inconstancy in their position, and anatomists are still undecided as to the normal,i.e.most frequent, arrangement of many of the smaller arteries. From a common-sense point of view it is probably of greater importance to realize how variable the distribution of small arteries is than to remember the names of twigs which are of neither surgical nor morphological importance. Arteries adapt themselves more quickly than most other structures to any mechanical obstruction, and many of the differences between the arterial systems of Man and other animals are due to the assumption of the erect position. Many arteries are tortuous, especially when they supply movable parts such as the face or scalp, but when one or two sharp bends are found they are generally due to the artery going out of its way to give off a constant and important branch. Small arteries unite or anastomose with others near them very freely, so that when even a large artery is obliterated a collateral circulation is carried on by the rapid increase in size of the communications between the branches coming off above and below the point of obstruction. Some branches, however, such as those going to the basal ganglia of the brain and to the spleen, are known as “end arteries,” and these do not anastomose with their neighbours at all; thus, if one is blocked, arterial blood is cut off from its area of supply. As a rule, there is little arterial anastomosis across the middle line of the body near the surface, though the scalp, lips and thyroid body are exceptions.
The distribution of the pulmonary artery is considered in connexion with the anatomy of the lungs (seeRespiratory System). That of the aorta will now be briefly described.TheAortalies in the cavities of the thorax and abdomen, and arises from the base of the left ventricle of the heart. It ascends forward, upward, and to the right as far as the level of the second right costal cartilage, then runs backward, andAorta.to the left to reach the left side of the body of the 4th thoracic vertebra, and then descends almost vertically. It thus forms thearch of the aorta, which arches over the root of the left lung, and which has attached to its concave surface a fibrous cord, known as the obliteratedductus arteriosus, which connects it with the left branch of the pulmonary artery. The aorta continues its course downward in close relation to the bodies of the thoracic vertebrae, then passes through an opening in the diaphragm (q.v.), enters the abdomen, and descends in front of the bodies of the lumbar vertebrae as low as the 4th, where it usually divides into two terminal branches, the common iliac arteries. Above and behind the angle of bifurcation, however, a long slender artery, called themiddle sacral, is prolonged downward in front of the sacrum to the end of the coccyx.It will be convenient to describe the distribution of the arteries under the following headings:—(1) Branches for the head, neck and upper limbs; (2) branches for the viscera of the thorax and abdomen; (3) branches for the walls of the thorax and abdomen; (4) branches for the pelvis and lower limbs.The branches for the head, neck and upper limbs arise as three large arteries from the transverse part of the aorta; they are namedinnominate, left common carotidandleft subclavian. The innominate artery is the largest and passes upward and to the right, to the root of the neck, where it divides into the right common carotid and the right subclavian. The carotid arteries supply the two sides of the head and neck; the subclavian arteries the two upper extremities.Thecommon carotidartery runs up the neck by the side of the windpipe, and on a level with the upper border of the thyroid cartilage divides into the internal and externalCarotid system.carotid arteries.Theinternal carotidartery ascends through the carotid canal in the temporal bone into the cranial cavity. It gives off anophthalmicbranch to the eyeball and other contents of the orbit, and then divides into theanteriorandmiddle cerebralarteries. The middle cerebral artery extends outward into the Sylvian fissure of the brain, and supplies the island of Reil, the orbital part, and the outer face of the frontal lobe, the parietal lobe, and the temporo-sphenoidal lobe; it also gives a choroid branch to the choroid plexus of the velum interpositum. The anterior cerebral artery supplies the inner face of the hemisphere from the anterior end of the frontal lobe as far back as the internal parieto-occipital fissure. At the base of the brain not only do the two internal carotids anastomose with each other through theanterior communicatingartery, which passes between their anterior cerebral branches, but the internal carotid on each side anastomoses with the posterior cerebral branch of the basilar, by aposterior communicatingartery. In this manner a vascular circle, thecircle of Willis, is formed, which permits of freedom of the arterial circulation by the anastomoses between arteries not only on the same side, but on opposite sides of the mesial plane. The vertebral and internal carotid arteries, which are the arteries of supply for the brain, are distinguished by lying at some depth from the surface in their course to the organ, by having curves or twists in their course, and by the absence of large collateral branches.Theexternal carotidartery ascends through the upper part of the side of the neck, and behind the lower jaw into the parotid gland, where it divides into the internal maxillary and superficial temporal branches. This artery gives off the following branches:—(a)Superior thyroidto the larynx and thyroid body; (b)Lingualto the tongue and sublingual gland; (c)Facialto the face, palate, tonsil and sub-maxillary gland; (d)Occipitalto the sterno-mastoid muscle and back of the scalp; (e)Posterior auricularto the back of the ear and the adjacent part of the scalp; (f)Superficial temporalto the scalp in front of the ear, and by itstransverse facialbranch to the back part of the face; (g)Internal maxillary, givingmuscularbranches to the muscles of mastication,meningealbranches to the dura mater,dentalbranches to the teeth, and other branches to the nose, palate and tympanum; (h)Ascending pharyngeal, which gives branches to the pharynx, palate, tonsils and dura mater.Thesubclavianartery is the commencement of the great arterial trunk for the upper limb. It passes across the root of the neck and behind the clavicle, where it enters the armpit, and becomes theaxillaryartery; by that name it extendsSubclavian system.as far as the posterior fold of the axilla, where it enters the upper arm, takes the name of brachial, and courses as far as the bend of the elbow; here it bifurcates into theradialandulnararteries. From the subclavian part of the trunk the following branches arise:—(a)Vertebral, which enters the foramen at the root of the transverse process of the 6th cervical vertebra, ascends through the corresponding foramina in the vertebrae above, lies in a groove on the arch of the atlas, and enters the skull through the foramen magnum, where it joins its fellow to form thebasilarartery; it gives offmuscularbranches to the deep muscles of the neck,spinalbranches to the spinal cord,meningealbranches to the dura mater, and aninferior cerebellarbranch to the under surface of the cerebellum. Thebasilarartery, formed by the junction of the two vertebrals, extends from the lower to the upper border of the pons Varolii; it gives offtransversebranches to the pons,auditorybranchesto the internal ear,inferior cerebellarbranches to the under surface of the cerebellum, whilst it breaks up into four terminal branches, viz. twosuperior cerebellarto the upper surface of the cerebellum, and twoposterior cerebralwhich supply the tentorial and mesial aspects of the temporo-sphenoidal lobes, the occipital lobes, and the posterior convolutions of the parietal lobes. (b)Thyroid axis, which immediately divides into theinferior thyroid, thesupra-scapular, and thetransverse cervicalbranches; theinferior thyroidsupplies the thyroid body, and gives off anascending cervicalbranch to the muscles of the neck; thesupra-scapularsupplies the muscles on the dorsum scapulae; thetransverse cervicalsupplies the trapezius and the muscles attached to the vertebral border of the scapula. (c)Internal mammarysupplies the anterior surface of the walls of the chest and abdomen, and the upper surface of the diaphragm. (d)Superior intercostalsupplies the first intercostal space, and by its deepcervicalbranch the deep muscles of the back of the neck.Theaxillaryartery suppliesthoracicbranches to the wall of the chest, the pectoral muscles, and the fat and glands of the axilla; anacromio-thoracicto the parts about the acromion;anteriorandposterior circumflexbranches to the shoulder joint and deltoid muscle; asubscapularbranch to the muscles of the posterior fold of the axilla.Thebrachialartery suppliesmuscularbranches to the muscles of the upper arm; anutrientbranch to the humerus;superiorandinferior profundabranches and ananastomoticto the muscles of the upper arm and the region of the elbow joint.Theulnarartery extends down the ulnar side of the front of the fore-arm to the palm of the hand, where it curves outward toward the thumb, and anastomoses with the superficial volar or other branch of the radial artery to form thesuperficial palmar arch. In the fore-arm the ulnar gives off theinterosseousarteries, which supply the muscles of the fore-arm and givenutrientbranches to the bones; tworecurrentbranches to the region of the elbow;carpalbranches to the wrist joint: in the hand it gives adeepbranch to the deep muscles of the hand, and from the superficial arch arisedigitalbranches to the sides of the little, ring, and middle fingers, and the ulnar border of the index finger.Theradialartery extends down the radial side of the front of the fore-arm, turns round the outer side of the wrist to the back of the hand, passes between the 1st and 2nd metacarpal bones to the palm, where it joins the deep branch of the ulnar, and forms thedeep palmar arch. In the fore-arm it gives off arecurrentbranch to the elbow joint;carpalbranches to the wrist joint; andmuscularbranches, one of which, named superficial volar, supplies the muscle of the thumb and joins the ulnar artery: in the hand it gives off a branch to the thumb, and one to the radial side of the index,interosseousbranches to the interosseous muscles,perforatingbranches to the back of the hand, andrecurrentbranches to the wrist.The branches of the aorta which supply the viscera of the thorax are the coronary, the oesophageal, the bronchial and the pericardiac. Thecoronaryarteries, two in number, are the first branches of the aorta, and arise opposite the anterior and leftVisceral branches.posterior segments of the semilunar valve, from the wall of the aorta, where it dilates into the sinuses of Valsalva. They supply the tissue of the heart.Theoesophageal,bronchialandpericardiacbranches are sufficiently described by their names.The branches of the aorta which supply the viscera of the abdomen arise either singly or in pairs. The single arteries are the coeliac axis, the superior mesenteric, and the inferior mesenteric, which arise from the front of the aorta; the pairs are the capsular, the two renal, and the two spermatic or ovarian, which arise from its sides. The single arteries supply viscera which are either completely or almost completely invested by the peritoneum, and the veins corresponding to them are the roots of the vena portae. The pairs of arteries supply viscera developed behind the peritoneum, and the veins corresponding to them are rootlets of the inferior vena cava.Thecoeliac axisis a thick, short artery, which almost immediately divides into the gastric, hepatic and splenic branches. Thegastricgives off oesophageal branches and then runs along the lesser curvature of the stomach. Thehepaticartery ends in the substance of the liver; but gives off acysticbranch to the gall bladder, apyloricbranch to the stomach, agastro-duodenalbranch, which divides into asuperior pancreatico-duodenalfor the pancreas and duodenum, and aright gastro-epiploicfor the stomach and omentum. Thesplenicartery ends in the substance of the spleen; but gives offpancreaticbranches to the pancreas,vasa breviato the left end of the stomach, and aleft gastro-epiploicto the stomach and omentum.Thesuperior mesentericartery gives off aninferior pancreatico-duodenalbranch to the pancreas and duodenum; about twelveintestinalbranches to the small intestines, which form in the substance of the mesentery a series of arches before they end in the wall of the intestines; anileocolicbranch to the end of the ileum, the caecum, and beginning of the colon; aright colicbranch to the ascending colon; and amiddle colicbranch to the transverse colon.Theinferior mesentericartery gives off aleft colicbranch to the descending colon, asigmoidbranch to the iliac and pelvic colon, and ends in the superiorhaemorrhoidalartery, which supplies the rectum. The arteries which supply the coats of the alimentary tube from the oesophagus to the rectum anastomose freely with each other in the wall of the tube, or in its mesenteric attachment, and the anastomoses are usually by the formation of arches or loops between adjacent branches.Thecapsular arteries, small in size, run outward from the aorta to end in the supra-renal capsules.Therenalarteries pass one to each kidney, in which they for the most part end, but in the substance of the organ they give off smallperforatingbranches, which pierce the capsule of the kidney, and are distributed in the surrounding fat. Additional renal arteries are fairly common.Thespermaticarteries are two long slender arteries, which descend, one in each spermatic cord, into the scrotum to supply the testicle. The corresponding ovarian arteries in the female do not leave the abdomen.The branches of the aorta which supply the walls of the thorax, abdomen and pelvis, are the intercostal, theParietal branches.lumbar, the phrenic, and the middle sacral.Fig.1.—Diagram of a pair of intercostal arteries.Ao, The aorta transversely divided, giving off at each side an intercostal artery.PB, The posterior or dorsal branch.AB, The anterior or proper intercostal branch.IM, A transverse section through the internal mammary artery.Theintercostalarteries arise from the back of the thoracic aorta, and are usually nine pairs. They run round the sides of the vertebral bodies as far as the commencement of the intercostal spaces, where each divides into adorsaland aproper intercostalbranch; the dorsal branch passes to the back of the thorax to supply the deep muscles of the spine; the proper intercostal branch (AB.) runs outward in the intercostal space to supply its muscles, and the lower pairs of intercostals also give branches to the diaphragm and wall of the abdomen. Below the last rib a subcostal artery runs.Thelumbararteries arise from the back of the abdominal aorta, and are usually four pairs. They run round the sides of the lumbar vertebrae, and divide into adorsalbranch which supplies the deep muscles of the back of the loins, and anabdominalbranch which runs outward to supply the wall of the abdomen. The distribution of the lumbar and intercostal arteries exhibits a transversely segmented arrangement of the vascular system, like the transversely segmented arrangement of the bones, muscles and nerves met with in these localities, but more especially in the thoracic region.Thephrenicarteries, two in number, pass to supply the under surface of the diaphragm.Themiddle sacralartery, as it runs down the front of the sacrum, gives branches to the back of the pelvic wall.Injections made by Sir W. Turner have shown that, both in the thoracic and abdominal cavities, slender anastomosing communications exist between the visceral and parietal branches.The arteries to the pelvis and hind limbs begin at the bifurcation of the aorta into the two common iliacs.Thecommon iliacartery, after a short course, divides into the internal and external iliac arteries. Theinternal iliacenters the pelvis and divides into branches for the supply of the pelvic walls and viscera, including the organs of generation, and for theIliac system.great muscles of the buttock. Theexternal iliacdescends behind Poupart’s ligament into the thigh, where it takes the name offemoralartery. The femoral descends along the front and inner surface of the thigh, gives off aprofundaor deep branch, which, by itscircumflexandperforatingbranches, supplies the numerous muscles of the thigh; most of these extend to the back of the limb to carry blood to the muscles situated there. The femoral artery then runs to the back of the limb in the ham, where it is calledpoplitealartery. The popliteal divides into two branches, of which one, calledanterior tibial, passes between the bones to the front of the leg, and then downward to the upper surface of the foot; the other,posterior tibial, continues down the back of the leg to the sole of the foot, and divides into theinternalandexternal plantararteries; branches proceed from the external plantar artery to the sides of the toes, and constitute thedigitalarteries. From the large arterial trunks in the leg many branches proceed, to carry blood to the different structures in the limb.The wall of an artery consists of several coats (see fig. 2). The outermost is thetunica adventitia, composed of connective tissue; immediately internal to this is theyellow elasticcoat; within this again themuscular coat, formed of involuntary.Structure of arteries.muscular tissue, the contractile fibre-cells of which are for the most part arranged transversely to the long axis of the artery; in the larger arteries the elastic coat is much thicker than the muscular, but in the smaller the muscular coat is relatively strong; the vaso-motor nerves terminate in the muscular coat. In the first part of the aorta, pulmonary artery and arteries of the retina there is no muscular coat. Internal to the muscular coat is theelastic fenestrated coat, formed of a smooth elastic membraneperforated by small apertures. Most internal of all is a layer ofendothelial cells, which form the free surface over which the blood flows. The arteries are not nourished by the blood which flows through them, but by minute vessels,vasa vasorum, distributed in their external, elastic and muscular coats.Fig.2.—Diagram of the structure of an artery. A, tunica adventitia; E, elastic coat; M, muscular coat; F, fenestrated coat; En, endothelium continuous with the endothelial wall of C, the capillaries.EmbryologyFig.3.—Diagram of the Embryonic Arterial Arches. 1, 2, 3, 4, 5, 6, point to the six arches. (The black parts are obliterated in the adult human subject.)V.Ao. Ventral Aorta.A.Ao. Arch of Aorta.D.Ar. Ductus Arteriosus.In. Innominate Artery.R.I.C.-L.I.C. Right and Left Internal Carotid Arteries.D.B. Duct of Botalli.R.S.-L.S. Right and Left Subclavian Arteries.R.V.-L.V. Right and Left Vertebral Arteries.P.A. Posterior Auricular Artery.Oph. Ophthalmic Artery.D.Ao. Dorsal Aorta.P.T. Pulmonary trunk.R.P.A.-L.P.A. Right and Left Pulmonary Arteries.R.C.C.-L.C.C. Right and Left Common Carotid Arteries.E.C. External Carotid Artery.Oc. Occipital Artery.I.M. Internal Maxillary Artery.Fig.4.—Diagram of the Human Aorta and its branches. S.T., Superficial Temporal Artery.The earliest appearance of the blood vessels is dealt with underVascular System. Here will be briefly described the fate of the main vessel which carries the blood away from the truncus arteriosus of the developing heart (q.v.). This ventral aorta, if traced forward, soon divides into two lateral parts, the explanation being that there were originally two vessels, side by side, which fused to form the heart, but continued separate anteriorly. The two parts run for a little distance toward the head of the embryo, ventral to the alimentary canal, and then turn toward the dorsum, passing one on either side of that tube to form the first aortic arch. Having reached the dorsum they turn backward toward the tail end and form the dorsal aortae; here, according to A.H. Young (Studies in Anatomy, Owens College, 1891 and 1900) they again turn toward the ventral side and become, after a transitional stage, thehypogastric, placental, allantoicorumbilicalarteries. This authority does not believe that the middle sacral artery of the adult is the real continuation of the single median dorsal aorta into which the two parallel dorsal vessels just mentioned soon coalesce, though until recently it has always been so regarded. The anterior loop between the ventral and dorsal aortae already described as the first aortic arch is included in themaxillaryorfirst visceral archof the soft parts (see fig. 3,1). Later, four other well-marked aortic arches grow behind this in the more caudal visceral arches, so that there are altogether five arterial arches on each side of the pharynx, through which the blood can pass from the ventral to the dorsal aorta. Of these arches the first soon disappears, but is probably partly represented in the adult by theinternal maxillaryartery, one branch of which, theinfraorbital, is enclosed in the upper jaw, while another, theinferior dental, is surrounded by the lower jaw. Possibly the ophthalmic artery also belongs to this arch. The second arch also disappears, but theposterior auricularandoccipitalarteries probably spring from it, and at an early period it passed through the stapes as the transitory stapedial artery. The third arch forms the beginning of the internal carotid. The fourth arch becomes the arch of the adult aorta, between the origins of the left carotid and left subclavian, on the left side, and the first part of the right subclavian artery on the right. The apparent fifth arch on the left side (fig. 3,6) remains all through foetal life as theductus arteriosus, and, as the lungs develop, thepulmonaryarteries are derived from it. J.E.V. Boas and W. Zimmermann have shown that this arch is in reality the sixth, and that there is a very transitory true fifth arch in front of it (fig. 3,5). The part of the ventral aorta from which this last arch rises is a single median vessel due to the same fusion of the two primitive ventral aortae which precedes the formation of the heart, but a spiral septum has appeared in it which divides it in such a way that while the anterior or cephalic arches communicate with the left ventricle of the heart, the last one communicates with the right (seeHeart). The fate of the ventral and dorsal longitudinal vessels must now be followed. The fused part of the two ventral aortae, just in front of the heart, forms the ascending part of the adult aortic arch, and where this trunk divides between the fifth and fourth arches (strictly speaking, the sixth and fifth), the right one forms theinnominate(fig. 3, In.) and the left one a very short part of thetransverse archof the aorta until the fourth arch comes off (see fig. 4). From this point to the origin of the third arch iscommon carotid, and after that, to the head,external carotidon each side. Thedorsal longitudinalarteries on the head side of the junction with the third arch form theinternal carotids. Between the third and fourth arches they are obliterated, while on the caudal side of this, until the point of fusion is reached on the dorsal side of the heart, the left artery forms the upper part of the dorsal aorta while the right entirely disappears. Below this point thethoracicandabdominal aortaeare formed by the twoprimitive dorsal aortaewhich have fused to form a single median vessel. As the limbs are developed, vessels bud out in them. Thesubclavianfor the arm comes from the fourth aortic arch on each side, while in the leg the main artery is a branch of thecaudal archwhich is curving ventralward to form the umbilical artery. From the convexity of this arch the internal iliac and sciatic at first carry the blood to the limb, as they do permanently in reptiles, but later the external iliac and femoral become developed, and, as they are on the concave side of the bend of the hip, while the sciatic is on the convex, they have a mechanical advantage and become the permanent main channel.For further details see O. Hertwig,Handbuch der vergleichenden und experimentellen Entwickelungslehre der Wirbeltiere(Jena, 1905).Comparative AnatomyIn the Acrania the lancelet (Amphioxus) shows certain arrangements of its arteries which are suggestive of the embryonic stages of the higher vertebrates and Man. There is a median ventral aorta below the pharynx, from which branchial arteries run up on each side between the branchial clefts, where the blood is aerated, to join two dorsal aortae which run back side by side until the hind end of the pharynx is reached; here they fuse to form a median vessel from which branches are distributed to the straight intestine. There is no heart, but the ventral aorta is contractile, and the blood is driven forward in it and backward in the dorsal aortae. The branchial arteries are very numerous, and cannot be homologized closely with the five (originally six) pairs of aortic arches in Man.In the fish the ventral aorta gives rise to five afferent branchial arteries carrying the blood to the gills, though these may not all come off as independent trunks from the aorta. From the gills the afferent branchials carry the blood to the median dorsal aorta. As pectoral and pelvic fins are now developed, subclavian and iliac arteries are found rising from the dorsal aorta, though the aorta itself is continued directly backward as the caudal artery into the tail. In the Dipnoi or mud fish, in which the swim bladder is converted into a functional lung, the hindmost afferent branchial artery, corresponding to the fifth (strictly speaking the sixth) aortic arch of the human embryo, gives off on each side a pulmonary artery to that structure.The arrangement of the branchial aortic arches in the tailed Amphibia (Urodela), and in the tadpole stage of the tailless forms (Anura), makes it probable that the generalized vertebrate has six (if not more) pairs of these instead of the five which are evident in the human embryo. Four pairs of arches are present, the first of which is the carotid and corresponds to the third of Man; the second is the true aortic arch on each side; the third undergoesgreat reduction or disappears when the gills atrophy, and is very transitory in the Mammalia (fig. 3,5), while the fourth is the one from which the pulmonary artery is developed when the lungs appear, and corresponds to the nominal fifth, though really the sixth arch, of the higher forms (fig. 3,6). The dorsal part of this sixth arch remains as a pervious vessel in the Urodela, joining the pulmonary arch to the dorsal aorta. In the central part of the carotid arch the vessel breaks up into a plexus, for a short distance forming the so-called carotid gland, which has an important effect upon the adult circulation of the Amphibia. In the Reptilia the great arteries are arranged on the same plan as in the adult Amphibia, but the carotid arch retains its dorsal communication with the systematic aortic arch on each side, and this communication is known as the duct of Botalli (fig. 3, D.B.). In this class, as in the Amphibia, one great artery, the coeliaco-mesenteric, usually supplies the liver, spleen, stomach and anterior part of the intestines; this is a point of some interest when it is noticed how very close together the coeliac axis and superior mesenteric arteries rise from the abdominal aorta in Man.In the Birds the right fourth arch alone remains as the aorta, the dorsal part of the left corresponding arch being obliterated. From the arch of the aorta rise two symmetrical innominates, each of which divides later into a carotid and subclavian. The blood path from the aorta to the hind limb in the Amphibia, Reptilia and Aves, is a dorsal one, and passes through the internal iliac and sciatic to the back of the thigh, and so to the popliteal space; the external iliac is, if it is developed at all, only a small branch to the pelvis.In the Mammalia the fourth left arch becomes the aorta, the corresponding right one being obliterated, but several cases have been recorded in Man in which both arches have persisted, as they do in the reptiles (H. Leboucq,Ann. Sci. Med. Gand, 1894, p. 7). Examples have also been found of a right aortic arch, as in birds, while a very common human abnormality is that in which the dorsal part of the fourth right arch persists, and from it the right subclavian artery arises (see fig. 3).The commonest arrangement of the great branches of the aortic arch in Mammals is that in which the innominate and left carotid arise by a single short trunk, while the left subclavian comes off later; this is also Man’s commonest abnormality. Sometimes, especially among the Ungulata, all the branches may rise from one common trunk; at other times two innominate arteries may be present; this is commonest in the Cheiroptera, Insectivora and Cetacea. It is extremely rare to find all four large arteries rising independently from the aorta, though it has been seen in the Koala (F.G. Parsons, “Mammalian Aortic Arch,”Journ. of Anat.vol. xxxvi. p. 389). The human arrangement of the common iliacs is not constant among mammals, for in some the external and internal iliacs rise independently from the aorta, and this is probably the more primitive arrangement. The middle sacral artery has already been referred to. A.H. Young and A. Robinson believe, on embryological grounds, that this artery in mammals is not homologous with the caudal artery of the fish, and is not the direct continuation of the aorta; it is an artery which usually gives off two or more collateral branches, and sometimes, as in the Ornithorynchus and some edentates, breaks up into a network of branches which reunite and so form what is known as arete mirabile. These retia mirabilia are often found in other parts of the mammalian body, though their function is still not satisfactorily explained. The way in which the blood is carried to the foot in the pronograde mammals differs from that of Man; a large branch called the internal saphenous comes off the common femoral in the lower third of the thigh, and this runs down the inner side of the leg to the foot. This arrangement is quite convenient as long as the knee is flexed, but when it comes to be extended, as in the erect posture, the artery is greatly stretched, and it is much easier for the blood to pass to the foot through the anterior and posterior tibials. A vestige of this saphenous artery, however, remains in Man as the anastomotica magna.The literature of the Comparative Anatomy of the Arteries up to 1902 will be found in R. Wiedersheim’sVergleichende Anatomie der Wirbeltiere(Jena, 1902). The morphology of the Iliac Arteries is described by G. Levi,Archivio Italiano di Anat. ed Embriol., vol. i. (1902).
The distribution of the pulmonary artery is considered in connexion with the anatomy of the lungs (seeRespiratory System). That of the aorta will now be briefly described.
TheAortalies in the cavities of the thorax and abdomen, and arises from the base of the left ventricle of the heart. It ascends forward, upward, and to the right as far as the level of the second right costal cartilage, then runs backward, andAorta.to the left to reach the left side of the body of the 4th thoracic vertebra, and then descends almost vertically. It thus forms thearch of the aorta, which arches over the root of the left lung, and which has attached to its concave surface a fibrous cord, known as the obliteratedductus arteriosus, which connects it with the left branch of the pulmonary artery. The aorta continues its course downward in close relation to the bodies of the thoracic vertebrae, then passes through an opening in the diaphragm (q.v.), enters the abdomen, and descends in front of the bodies of the lumbar vertebrae as low as the 4th, where it usually divides into two terminal branches, the common iliac arteries. Above and behind the angle of bifurcation, however, a long slender artery, called themiddle sacral, is prolonged downward in front of the sacrum to the end of the coccyx.
It will be convenient to describe the distribution of the arteries under the following headings:—(1) Branches for the head, neck and upper limbs; (2) branches for the viscera of the thorax and abdomen; (3) branches for the walls of the thorax and abdomen; (4) branches for the pelvis and lower limbs.
The branches for the head, neck and upper limbs arise as three large arteries from the transverse part of the aorta; they are namedinnominate, left common carotidandleft subclavian. The innominate artery is the largest and passes upward and to the right, to the root of the neck, where it divides into the right common carotid and the right subclavian. The carotid arteries supply the two sides of the head and neck; the subclavian arteries the two upper extremities.
Thecommon carotidartery runs up the neck by the side of the windpipe, and on a level with the upper border of the thyroid cartilage divides into the internal and externalCarotid system.carotid arteries.
Theinternal carotidartery ascends through the carotid canal in the temporal bone into the cranial cavity. It gives off anophthalmicbranch to the eyeball and other contents of the orbit, and then divides into theanteriorandmiddle cerebralarteries. The middle cerebral artery extends outward into the Sylvian fissure of the brain, and supplies the island of Reil, the orbital part, and the outer face of the frontal lobe, the parietal lobe, and the temporo-sphenoidal lobe; it also gives a choroid branch to the choroid plexus of the velum interpositum. The anterior cerebral artery supplies the inner face of the hemisphere from the anterior end of the frontal lobe as far back as the internal parieto-occipital fissure. At the base of the brain not only do the two internal carotids anastomose with each other through theanterior communicatingartery, which passes between their anterior cerebral branches, but the internal carotid on each side anastomoses with the posterior cerebral branch of the basilar, by aposterior communicatingartery. In this manner a vascular circle, thecircle of Willis, is formed, which permits of freedom of the arterial circulation by the anastomoses between arteries not only on the same side, but on opposite sides of the mesial plane. The vertebral and internal carotid arteries, which are the arteries of supply for the brain, are distinguished by lying at some depth from the surface in their course to the organ, by having curves or twists in their course, and by the absence of large collateral branches.
Theexternal carotidartery ascends through the upper part of the side of the neck, and behind the lower jaw into the parotid gland, where it divides into the internal maxillary and superficial temporal branches. This artery gives off the following branches:—(a)Superior thyroidto the larynx and thyroid body; (b)Lingualto the tongue and sublingual gland; (c)Facialto the face, palate, tonsil and sub-maxillary gland; (d)Occipitalto the sterno-mastoid muscle and back of the scalp; (e)Posterior auricularto the back of the ear and the adjacent part of the scalp; (f)Superficial temporalto the scalp in front of the ear, and by itstransverse facialbranch to the back part of the face; (g)Internal maxillary, givingmuscularbranches to the muscles of mastication,meningealbranches to the dura mater,dentalbranches to the teeth, and other branches to the nose, palate and tympanum; (h)Ascending pharyngeal, which gives branches to the pharynx, palate, tonsils and dura mater.
Thesubclavianartery is the commencement of the great arterial trunk for the upper limb. It passes across the root of the neck and behind the clavicle, where it enters the armpit, and becomes theaxillaryartery; by that name it extendsSubclavian system.as far as the posterior fold of the axilla, where it enters the upper arm, takes the name of brachial, and courses as far as the bend of the elbow; here it bifurcates into theradialandulnararteries. From the subclavian part of the trunk the following branches arise:—(a)Vertebral, which enters the foramen at the root of the transverse process of the 6th cervical vertebra, ascends through the corresponding foramina in the vertebrae above, lies in a groove on the arch of the atlas, and enters the skull through the foramen magnum, where it joins its fellow to form thebasilarartery; it gives offmuscularbranches to the deep muscles of the neck,spinalbranches to the spinal cord,meningealbranches to the dura mater, and aninferior cerebellarbranch to the under surface of the cerebellum. Thebasilarartery, formed by the junction of the two vertebrals, extends from the lower to the upper border of the pons Varolii; it gives offtransversebranches to the pons,auditorybranchesto the internal ear,inferior cerebellarbranches to the under surface of the cerebellum, whilst it breaks up into four terminal branches, viz. twosuperior cerebellarto the upper surface of the cerebellum, and twoposterior cerebralwhich supply the tentorial and mesial aspects of the temporo-sphenoidal lobes, the occipital lobes, and the posterior convolutions of the parietal lobes. (b)Thyroid axis, which immediately divides into theinferior thyroid, thesupra-scapular, and thetransverse cervicalbranches; theinferior thyroidsupplies the thyroid body, and gives off anascending cervicalbranch to the muscles of the neck; thesupra-scapularsupplies the muscles on the dorsum scapulae; thetransverse cervicalsupplies the trapezius and the muscles attached to the vertebral border of the scapula. (c)Internal mammarysupplies the anterior surface of the walls of the chest and abdomen, and the upper surface of the diaphragm. (d)Superior intercostalsupplies the first intercostal space, and by its deepcervicalbranch the deep muscles of the back of the neck.
Theaxillaryartery suppliesthoracicbranches to the wall of the chest, the pectoral muscles, and the fat and glands of the axilla; anacromio-thoracicto the parts about the acromion;anteriorandposterior circumflexbranches to the shoulder joint and deltoid muscle; asubscapularbranch to the muscles of the posterior fold of the axilla.
Thebrachialartery suppliesmuscularbranches to the muscles of the upper arm; anutrientbranch to the humerus;superiorandinferior profundabranches and ananastomoticto the muscles of the upper arm and the region of the elbow joint.
Theulnarartery extends down the ulnar side of the front of the fore-arm to the palm of the hand, where it curves outward toward the thumb, and anastomoses with the superficial volar or other branch of the radial artery to form thesuperficial palmar arch. In the fore-arm the ulnar gives off theinterosseousarteries, which supply the muscles of the fore-arm and givenutrientbranches to the bones; tworecurrentbranches to the region of the elbow;carpalbranches to the wrist joint: in the hand it gives adeepbranch to the deep muscles of the hand, and from the superficial arch arisedigitalbranches to the sides of the little, ring, and middle fingers, and the ulnar border of the index finger.
Theradialartery extends down the radial side of the front of the fore-arm, turns round the outer side of the wrist to the back of the hand, passes between the 1st and 2nd metacarpal bones to the palm, where it joins the deep branch of the ulnar, and forms thedeep palmar arch. In the fore-arm it gives off arecurrentbranch to the elbow joint;carpalbranches to the wrist joint; andmuscularbranches, one of which, named superficial volar, supplies the muscle of the thumb and joins the ulnar artery: in the hand it gives off a branch to the thumb, and one to the radial side of the index,interosseousbranches to the interosseous muscles,perforatingbranches to the back of the hand, andrecurrentbranches to the wrist.
The branches of the aorta which supply the viscera of the thorax are the coronary, the oesophageal, the bronchial and the pericardiac. Thecoronaryarteries, two in number, are the first branches of the aorta, and arise opposite the anterior and leftVisceral branches.posterior segments of the semilunar valve, from the wall of the aorta, where it dilates into the sinuses of Valsalva. They supply the tissue of the heart.
Theoesophageal,bronchialandpericardiacbranches are sufficiently described by their names.
The branches of the aorta which supply the viscera of the abdomen arise either singly or in pairs. The single arteries are the coeliac axis, the superior mesenteric, and the inferior mesenteric, which arise from the front of the aorta; the pairs are the capsular, the two renal, and the two spermatic or ovarian, which arise from its sides. The single arteries supply viscera which are either completely or almost completely invested by the peritoneum, and the veins corresponding to them are the roots of the vena portae. The pairs of arteries supply viscera developed behind the peritoneum, and the veins corresponding to them are rootlets of the inferior vena cava.
Thecoeliac axisis a thick, short artery, which almost immediately divides into the gastric, hepatic and splenic branches. Thegastricgives off oesophageal branches and then runs along the lesser curvature of the stomach. Thehepaticartery ends in the substance of the liver; but gives off acysticbranch to the gall bladder, apyloricbranch to the stomach, agastro-duodenalbranch, which divides into asuperior pancreatico-duodenalfor the pancreas and duodenum, and aright gastro-epiploicfor the stomach and omentum. Thesplenicartery ends in the substance of the spleen; but gives offpancreaticbranches to the pancreas,vasa breviato the left end of the stomach, and aleft gastro-epiploicto the stomach and omentum.
Thesuperior mesentericartery gives off aninferior pancreatico-duodenalbranch to the pancreas and duodenum; about twelveintestinalbranches to the small intestines, which form in the substance of the mesentery a series of arches before they end in the wall of the intestines; anileocolicbranch to the end of the ileum, the caecum, and beginning of the colon; aright colicbranch to the ascending colon; and amiddle colicbranch to the transverse colon.
Theinferior mesentericartery gives off aleft colicbranch to the descending colon, asigmoidbranch to the iliac and pelvic colon, and ends in the superiorhaemorrhoidalartery, which supplies the rectum. The arteries which supply the coats of the alimentary tube from the oesophagus to the rectum anastomose freely with each other in the wall of the tube, or in its mesenteric attachment, and the anastomoses are usually by the formation of arches or loops between adjacent branches.
Thecapsular arteries, small in size, run outward from the aorta to end in the supra-renal capsules.
Therenalarteries pass one to each kidney, in which they for the most part end, but in the substance of the organ they give off smallperforatingbranches, which pierce the capsule of the kidney, and are distributed in the surrounding fat. Additional renal arteries are fairly common.
Thespermaticarteries are two long slender arteries, which descend, one in each spermatic cord, into the scrotum to supply the testicle. The corresponding ovarian arteries in the female do not leave the abdomen.
The branches of the aorta which supply the walls of the thorax, abdomen and pelvis, are the intercostal, theParietal branches.lumbar, the phrenic, and the middle sacral.
Ao, The aorta transversely divided, giving off at each side an intercostal artery.
PB, The posterior or dorsal branch.
AB, The anterior or proper intercostal branch.
IM, A transverse section through the internal mammary artery.
Theintercostalarteries arise from the back of the thoracic aorta, and are usually nine pairs. They run round the sides of the vertebral bodies as far as the commencement of the intercostal spaces, where each divides into adorsaland aproper intercostalbranch; the dorsal branch passes to the back of the thorax to supply the deep muscles of the spine; the proper intercostal branch (AB.) runs outward in the intercostal space to supply its muscles, and the lower pairs of intercostals also give branches to the diaphragm and wall of the abdomen. Below the last rib a subcostal artery runs.
Thelumbararteries arise from the back of the abdominal aorta, and are usually four pairs. They run round the sides of the lumbar vertebrae, and divide into adorsalbranch which supplies the deep muscles of the back of the loins, and anabdominalbranch which runs outward to supply the wall of the abdomen. The distribution of the lumbar and intercostal arteries exhibits a transversely segmented arrangement of the vascular system, like the transversely segmented arrangement of the bones, muscles and nerves met with in these localities, but more especially in the thoracic region.
Thephrenicarteries, two in number, pass to supply the under surface of the diaphragm.
Themiddle sacralartery, as it runs down the front of the sacrum, gives branches to the back of the pelvic wall.
Injections made by Sir W. Turner have shown that, both in the thoracic and abdominal cavities, slender anastomosing communications exist between the visceral and parietal branches.
The arteries to the pelvis and hind limbs begin at the bifurcation of the aorta into the two common iliacs.
Thecommon iliacartery, after a short course, divides into the internal and external iliac arteries. Theinternal iliacenters the pelvis and divides into branches for the supply of the pelvic walls and viscera, including the organs of generation, and for theIliac system.great muscles of the buttock. Theexternal iliacdescends behind Poupart’s ligament into the thigh, where it takes the name offemoralartery. The femoral descends along the front and inner surface of the thigh, gives off aprofundaor deep branch, which, by itscircumflexandperforatingbranches, supplies the numerous muscles of the thigh; most of these extend to the back of the limb to carry blood to the muscles situated there. The femoral artery then runs to the back of the limb in the ham, where it is calledpoplitealartery. The popliteal divides into two branches, of which one, calledanterior tibial, passes between the bones to the front of the leg, and then downward to the upper surface of the foot; the other,posterior tibial, continues down the back of the leg to the sole of the foot, and divides into theinternalandexternal plantararteries; branches proceed from the external plantar artery to the sides of the toes, and constitute thedigitalarteries. From the large arterial trunks in the leg many branches proceed, to carry blood to the different structures in the limb.
The wall of an artery consists of several coats (see fig. 2). The outermost is thetunica adventitia, composed of connective tissue; immediately internal to this is theyellow elasticcoat; within this again themuscular coat, formed of involuntary.Structure of arteries.muscular tissue, the contractile fibre-cells of which are for the most part arranged transversely to the long axis of the artery; in the larger arteries the elastic coat is much thicker than the muscular, but in the smaller the muscular coat is relatively strong; the vaso-motor nerves terminate in the muscular coat. In the first part of the aorta, pulmonary artery and arteries of the retina there is no muscular coat. Internal to the muscular coat is theelastic fenestrated coat, formed of a smooth elastic membraneperforated by small apertures. Most internal of all is a layer ofendothelial cells, which form the free surface over which the blood flows. The arteries are not nourished by the blood which flows through them, but by minute vessels,vasa vasorum, distributed in their external, elastic and muscular coats.
Embryology
V.Ao. Ventral Aorta.
A.Ao. Arch of Aorta.
D.Ar. Ductus Arteriosus.
In. Innominate Artery.
R.I.C.-L.I.C. Right and Left Internal Carotid Arteries.
D.B. Duct of Botalli.
R.S.-L.S. Right and Left Subclavian Arteries.
R.V.-L.V. Right and Left Vertebral Arteries.
P.A. Posterior Auricular Artery.
Oph. Ophthalmic Artery.
D.Ao. Dorsal Aorta.
P.T. Pulmonary trunk.
R.P.A.-L.P.A. Right and Left Pulmonary Arteries.
R.C.C.-L.C.C. Right and Left Common Carotid Arteries.
E.C. External Carotid Artery.
Oc. Occipital Artery.
I.M. Internal Maxillary Artery.
The earliest appearance of the blood vessels is dealt with underVascular System. Here will be briefly described the fate of the main vessel which carries the blood away from the truncus arteriosus of the developing heart (q.v.). This ventral aorta, if traced forward, soon divides into two lateral parts, the explanation being that there were originally two vessels, side by side, which fused to form the heart, but continued separate anteriorly. The two parts run for a little distance toward the head of the embryo, ventral to the alimentary canal, and then turn toward the dorsum, passing one on either side of that tube to form the first aortic arch. Having reached the dorsum they turn backward toward the tail end and form the dorsal aortae; here, according to A.H. Young (Studies in Anatomy, Owens College, 1891 and 1900) they again turn toward the ventral side and become, after a transitional stage, thehypogastric, placental, allantoicorumbilicalarteries. This authority does not believe that the middle sacral artery of the adult is the real continuation of the single median dorsal aorta into which the two parallel dorsal vessels just mentioned soon coalesce, though until recently it has always been so regarded. The anterior loop between the ventral and dorsal aortae already described as the first aortic arch is included in themaxillaryorfirst visceral archof the soft parts (see fig. 3,1). Later, four other well-marked aortic arches grow behind this in the more caudal visceral arches, so that there are altogether five arterial arches on each side of the pharynx, through which the blood can pass from the ventral to the dorsal aorta. Of these arches the first soon disappears, but is probably partly represented in the adult by theinternal maxillaryartery, one branch of which, theinfraorbital, is enclosed in the upper jaw, while another, theinferior dental, is surrounded by the lower jaw. Possibly the ophthalmic artery also belongs to this arch. The second arch also disappears, but theposterior auricularandoccipitalarteries probably spring from it, and at an early period it passed through the stapes as the transitory stapedial artery. The third arch forms the beginning of the internal carotid. The fourth arch becomes the arch of the adult aorta, between the origins of the left carotid and left subclavian, on the left side, and the first part of the right subclavian artery on the right. The apparent fifth arch on the left side (fig. 3,6) remains all through foetal life as theductus arteriosus, and, as the lungs develop, thepulmonaryarteries are derived from it. J.E.V. Boas and W. Zimmermann have shown that this arch is in reality the sixth, and that there is a very transitory true fifth arch in front of it (fig. 3,5). The part of the ventral aorta from which this last arch rises is a single median vessel due to the same fusion of the two primitive ventral aortae which precedes the formation of the heart, but a spiral septum has appeared in it which divides it in such a way that while the anterior or cephalic arches communicate with the left ventricle of the heart, the last one communicates with the right (seeHeart). The fate of the ventral and dorsal longitudinal vessels must now be followed. The fused part of the two ventral aortae, just in front of the heart, forms the ascending part of the adult aortic arch, and where this trunk divides between the fifth and fourth arches (strictly speaking, the sixth and fifth), the right one forms theinnominate(fig. 3, In.) and the left one a very short part of thetransverse archof the aorta until the fourth arch comes off (see fig. 4). From this point to the origin of the third arch iscommon carotid, and after that, to the head,external carotidon each side. Thedorsal longitudinalarteries on the head side of the junction with the third arch form theinternal carotids. Between the third and fourth arches they are obliterated, while on the caudal side of this, until the point of fusion is reached on the dorsal side of the heart, the left artery forms the upper part of the dorsal aorta while the right entirely disappears. Below this point thethoracicandabdominal aortaeare formed by the twoprimitive dorsal aortaewhich have fused to form a single median vessel. As the limbs are developed, vessels bud out in them. Thesubclavianfor the arm comes from the fourth aortic arch on each side, while in the leg the main artery is a branch of thecaudal archwhich is curving ventralward to form the umbilical artery. From the convexity of this arch the internal iliac and sciatic at first carry the blood to the limb, as they do permanently in reptiles, but later the external iliac and femoral become developed, and, as they are on the concave side of the bend of the hip, while the sciatic is on the convex, they have a mechanical advantage and become the permanent main channel.
For further details see O. Hertwig,Handbuch der vergleichenden und experimentellen Entwickelungslehre der Wirbeltiere(Jena, 1905).
Comparative Anatomy
In the Acrania the lancelet (Amphioxus) shows certain arrangements of its arteries which are suggestive of the embryonic stages of the higher vertebrates and Man. There is a median ventral aorta below the pharynx, from which branchial arteries run up on each side between the branchial clefts, where the blood is aerated, to join two dorsal aortae which run back side by side until the hind end of the pharynx is reached; here they fuse to form a median vessel from which branches are distributed to the straight intestine. There is no heart, but the ventral aorta is contractile, and the blood is driven forward in it and backward in the dorsal aortae. The branchial arteries are very numerous, and cannot be homologized closely with the five (originally six) pairs of aortic arches in Man.
In the fish the ventral aorta gives rise to five afferent branchial arteries carrying the blood to the gills, though these may not all come off as independent trunks from the aorta. From the gills the afferent branchials carry the blood to the median dorsal aorta. As pectoral and pelvic fins are now developed, subclavian and iliac arteries are found rising from the dorsal aorta, though the aorta itself is continued directly backward as the caudal artery into the tail. In the Dipnoi or mud fish, in which the swim bladder is converted into a functional lung, the hindmost afferent branchial artery, corresponding to the fifth (strictly speaking the sixth) aortic arch of the human embryo, gives off on each side a pulmonary artery to that structure.
The arrangement of the branchial aortic arches in the tailed Amphibia (Urodela), and in the tadpole stage of the tailless forms (Anura), makes it probable that the generalized vertebrate has six (if not more) pairs of these instead of the five which are evident in the human embryo. Four pairs of arches are present, the first of which is the carotid and corresponds to the third of Man; the second is the true aortic arch on each side; the third undergoesgreat reduction or disappears when the gills atrophy, and is very transitory in the Mammalia (fig. 3,5), while the fourth is the one from which the pulmonary artery is developed when the lungs appear, and corresponds to the nominal fifth, though really the sixth arch, of the higher forms (fig. 3,6). The dorsal part of this sixth arch remains as a pervious vessel in the Urodela, joining the pulmonary arch to the dorsal aorta. In the central part of the carotid arch the vessel breaks up into a plexus, for a short distance forming the so-called carotid gland, which has an important effect upon the adult circulation of the Amphibia. In the Reptilia the great arteries are arranged on the same plan as in the adult Amphibia, but the carotid arch retains its dorsal communication with the systematic aortic arch on each side, and this communication is known as the duct of Botalli (fig. 3, D.B.). In this class, as in the Amphibia, one great artery, the coeliaco-mesenteric, usually supplies the liver, spleen, stomach and anterior part of the intestines; this is a point of some interest when it is noticed how very close together the coeliac axis and superior mesenteric arteries rise from the abdominal aorta in Man.
In the Birds the right fourth arch alone remains as the aorta, the dorsal part of the left corresponding arch being obliterated. From the arch of the aorta rise two symmetrical innominates, each of which divides later into a carotid and subclavian. The blood path from the aorta to the hind limb in the Amphibia, Reptilia and Aves, is a dorsal one, and passes through the internal iliac and sciatic to the back of the thigh, and so to the popliteal space; the external iliac is, if it is developed at all, only a small branch to the pelvis.
In the Mammalia the fourth left arch becomes the aorta, the corresponding right one being obliterated, but several cases have been recorded in Man in which both arches have persisted, as they do in the reptiles (H. Leboucq,Ann. Sci. Med. Gand, 1894, p. 7). Examples have also been found of a right aortic arch, as in birds, while a very common human abnormality is that in which the dorsal part of the fourth right arch persists, and from it the right subclavian artery arises (see fig. 3).
The commonest arrangement of the great branches of the aortic arch in Mammals is that in which the innominate and left carotid arise by a single short trunk, while the left subclavian comes off later; this is also Man’s commonest abnormality. Sometimes, especially among the Ungulata, all the branches may rise from one common trunk; at other times two innominate arteries may be present; this is commonest in the Cheiroptera, Insectivora and Cetacea. It is extremely rare to find all four large arteries rising independently from the aorta, though it has been seen in the Koala (F.G. Parsons, “Mammalian Aortic Arch,”Journ. of Anat.vol. xxxvi. p. 389). The human arrangement of the common iliacs is not constant among mammals, for in some the external and internal iliacs rise independently from the aorta, and this is probably the more primitive arrangement. The middle sacral artery has already been referred to. A.H. Young and A. Robinson believe, on embryological grounds, that this artery in mammals is not homologous with the caudal artery of the fish, and is not the direct continuation of the aorta; it is an artery which usually gives off two or more collateral branches, and sometimes, as in the Ornithorynchus and some edentates, breaks up into a network of branches which reunite and so form what is known as arete mirabile. These retia mirabilia are often found in other parts of the mammalian body, though their function is still not satisfactorily explained. The way in which the blood is carried to the foot in the pronograde mammals differs from that of Man; a large branch called the internal saphenous comes off the common femoral in the lower third of the thigh, and this runs down the inner side of the leg to the foot. This arrangement is quite convenient as long as the knee is flexed, but when it comes to be extended, as in the erect posture, the artery is greatly stretched, and it is much easier for the blood to pass to the foot through the anterior and posterior tibials. A vestige of this saphenous artery, however, remains in Man as the anastomotica magna.
The literature of the Comparative Anatomy of the Arteries up to 1902 will be found in R. Wiedersheim’sVergleichende Anatomie der Wirbeltiere(Jena, 1902). The morphology of the Iliac Arteries is described by G. Levi,Archivio Italiano di Anat. ed Embriol., vol. i. (1902).