Fam. 2. Delphinidae.—This family, which includes the greater number of Cetacea, may thus be characterised:—Whales of small to moderate size. Teeth as a rule numerous, and present in the upper as well as in the lower jaw. Maxillae without large crests; the pterygoids, often meeting in the middle line, enclose an air space open behind. The anterior (five to eight) ribs are two headed, the posterior with tubercular head only. The sternal ribs are ossified.
The Dolphins and Porpoises, as already stated, embrace the greater number of existing species of Whales. Sir W. Flower and others who have followed him, allow nineteen genera. But as to the exact number of known species there is much uncertainty. That very careful observer, Mr. True, considers[246]that there are fifty which demand recognition. As many as one hundred have received names. The matter is one which is perhaps barely ripe for decision. All the Dolphin tribe are, for Whales, smallish animals. The Killer Whale,Orca, is the only genus (or species?) which usually attains to more than moderate bulk. The rather mysteriousDelphinus coronatus, 36 feet in length, of M. de Fréminville, would seem to be a Ziphioid; it was described as having a very pointed beak, and as having the dorsal fin situated near the tail; such characters suggest aMesoplodon.
The genusDelphinapterus, the Beluga or White Whale, consists of but a single species, though as usual more than one name has been given to supposed different species. It is characterised as a genus by the following assemblage of structural features:—It has only eight to ten teeth occupying the anterior part of the jaws only. All the cervical vertebrae are free and unjoined. The vertebral formula is C 7, D 11 (or 12), L 9, Ca 23. The pterygoids are wide apart, though they converge as if about to meet at their posterior ends. There is no dorsal fin. The colour is white.
The Beluga is a northern species purely. The reputed form,D. kingii, was said to come from Australian seas; but there seems to have been an error in this statement. It is interesting to note that the white colour, so characteristic of the genus and species, is not found in the young, which are blackish. They gradually pale as they advance towards maturity.Delphinapterus leucasreaches a length of 10 feet, and like other Porpoises will ascend rivers in search of food. It is said to be specially addicted to salmon. Among the contents of the stomach have been found quantities of sand. But this habit of swallowing sand or pebbles has been noted in other Whales. Whether it is or is not accidental (taken in with ground-living food), it seems hardly likely that it is used for purposes of ballast! The Beluga has a voice; but the name "Sea Canary" is hardly suitable to it. A specimen of this species, recently described from the shores of Scotland (it is often thrown up upon our coasts), which had got entangled in the stakes of a new net, was regarded by the natives, on account of its white colour, as a ghost. Externally, besides its colour, the Beluga is remarkable for possessing a distinct neck, which is correlated of course with the freedom of the cervical vertebrae, and is also seen in Platanistidae.
The Narwhal (Monodon) is closely allied in structure to the last genus. It has the following anatomical characters:—The teeth are reduced to a single "horn" in the upper jaw, which is rudimentary in the female. The neck vertebrae are free. The vertebral formula is C 7, D 11, L 6, Ca 26. The pterygoids are as inDelphinapterus, and, as in that genus, there are no hairs upon the face or dorsal fin.
This genus is of course most obviously characterised by the twisted tusk of the male, which is occasionally double. This tusk has given to the only species of the genus,M. monoceros, both its generic and specific name. The animal has a spotted colour; but, as in the case of the Beluga, old animals tend to become white. The use of its horn toMonodonhas been debated. In the first place it is clearly a secondary sexual character. The males have been observed to cross their horns like rapiers in a fencing match. It may be that they are used in more serious combats. An ingenious suggestion is that the long and strong tusk enables its possessor to break the thick ice andmake a breathing hole. A third suggestion is due to Scoresby, who was led to make it from having taken out of the stomach of a Narwhal a large skate. He held that with its tusk the Whale empaled the fish and then swallowed it. The Narwhal is not large, 15 feet or so in length. But Lacepède, who was apt to compile with lack of discrimination, speaks of 60 feet long Narwhals.Monodonis purely Arctic, and but three or four specimens have ever been cast up on our shores.
Of true Porpoises, genusPhocaena, there are apparently several species. The genus itself has the following characters:—The teeth are sixteen to twenty-six on each half of each jaw; their crowns are compressed and lobed. The pterygoids do not meet. The dorsal fin has a row of tubercles along its margin.
The Porpoise of our coasts,P. communis, is a smallish species 6 to 8 feet in length. There are two to four hairs present in the young; its colour is black, generally lighter on the belly. The first six cervical vertebrae are fused. The ribs vary in number from twelve to fourteen pairs. It is a gregarious Whale, and will ascend rivers; it has been seen for example in the Seine at Paris. The name Porpoise is often written Porkpisce, which of course shows its origin. Very conveniently it was regarded as a fish, and therefore allowed to be eaten in Lent. The celebrated Dr. Caius, a gourmet as well as a physician and the refounder of a college, invented a particular sauce wherewith to dress this royal dish. Some time since Dr. Gray described a Porpoise from Margate as a distinct species (see p.342) on account of the tubercles, which are now known to be a generic character.
Dr. Burmeister'sP. spinipennisseems, however, to be really distinct. It was captured near the mouth of the Rio de la Plata. It is more tuberculated on the fin and back, and has fewer teeth (sixteen as against twenty-six).
Mr. True'sP. dalliiof the Pacific (where the Common Porpoise also occurs) is characterised chiefly by its very long vertebral column, consisting of ninety-eight vertebrae; there are only sixty-eight in the other species. The Eastern genusNeomerisis placed withPhocaenaby Dr. Blanford. It practically only differs by the absence of a dorsal fin. It is only about 4 feet long, and inhabits the seas of India, Cape of Good Hope, and Japan. The one species is calledN. phocaenoides.
The genusGlobicephalusis to be defined thus:—Teethseven to twelve on each side, confined to anterior end of jaws. Skull raised into a prominence behind the blow-hole; pterygoids large and in contact. Pectoral fin long and falcate; dorsal fin present. No beak. Vertebral formula C 7, D 11, L 11 to 14, Ca 27 to 29. Six pairs of the ribs are two-headed.
The best known species of the genus is the Ca'ing Whale,G. melas.[247]This animal reaches a length of 20 feet, and is thus one of the largest of the Delphinidae. It is gregarious and was, even is now, much hunted in the Faeroe Islands. Its sheep-like habits (embodied in one scientific namedeductor) enable it to be easily driven on shore in herds, which are then harpooned. The foetus of this Whale has a few hairs; the number of phalanges in the two middle digits is very great, as many as eleven to fourteen.G. scammoni,G. brachypterus, andG. indicusare other reputed species of the genus allowed by True and Blanford.
Grampusis a genus allied to the last. It has no teeth in the upper jaw, and but three to seven in the lower jaw, near the symphysis of the mandible. The pterygoids are in contact. There is no beak, and the pectoral fin is long. There are twelve pairs of ribs, of which six are two-headed. Apparently there is but one species,G. griseus, known as "Risso's Dolphin." It is a Mediterranean and Atlantic form, and is not common.
The genusOrcahas as characters:—Teeth ten to thirteen, long and strong. Pterygoids not quite meeting. Vertebrae C 7, D 11 to 12, L 10, Ca 23. The first two or three fused. The dorsal fin is long and pointed.
Of this genus there may be more than one species; but the best known is the Killer Whale,O. gladiator(Fig. 180, p.341), often spoken of as the "Grampus."[248]It is marked with contrasting bands of white or yellow upon a black body-colour. The animal grows to a considerable length, as much as 30 feet.Orcais a powerful and rapacious Whale; and Eschricht has stated that from the stomach of one, thirteen Porpoises and fourteen Seals were extracted. They will also combine to attack larger Whales, and Scammon has related how he witnessed such an onslaught upon a CalifornianGrey Whale. "Belua truculenta dentibus," observed Olaus Magnus of this Cetacean. The high dorsal fin has been much exaggerated in old drawings; it has been even represented as strong and sharpened at the end, so as to be capable of ripping open the belly of a Whale. The fact that it sometimes lies over a little to one side is responsible for another anecdote: that an example of this Whale was seen to retire with a couple of Seals tucked away under the flippers, another grasped by the dorsal fin, and a fourth in the mouth! "When an Orca pursues a whale," wrote Dr. Frangius, "the latter makes a terrible bellowing like a bull when bitten by a dog." It is probable, according to F. Cuvier, that this Whale is the "Aries marinus" of the ancients, certain bands of white upon the head giving an impression of curved horns. It may also be the "horrible Sea-satyre" of Edmund Spencer.
Allied toOrca, but distinguishable from it by some rather minute peculiarities, isPseudorca. It may be thus defined:—Teeth eight to ten, much like those ofOrca. Dorsal fin rather small, falcate. Vertebral formula C 7, D 10, L 9, Ca 24. Six or all the cervicals united. The curious fact about this Whale, which embraces only a single species,P. crassidens, is that it was first known in the fossil condition from remains discovered in the fens of Lincolnshire. An important day for cetologists was that on which a whole herd entered the Baltic and furnished material for a better study of this Whale. It is not, any more than its near allyOrca, confined to northern seas; for several examples, at first relegated to a distinct species (P. meridionalis), have been obtained from the seas round Tasmania.
Orcella(which has been writtenOrcaella) has fourteen to nineteen small sharp teeth in each half of each jaw. The pterygoids are widely separate. The dorsal fin is small and falcate. The vertebral formula is C 7, D 14, L 14, Ca 26. Seven ribs are two-headed, and five of them reach the sternum.
This genus contains but a single species,O. brevirostris, which is both marine and fresh-water in habit; it occurs in the Indian seas, and in the Irrawaddy even as far up as 900 miles from the sea. Some regard the fresh-water individuals as a distinct form,O. fluminalis.
Sagmatiasis a genus known only from a skull, which is remarkable for the elevation of the premaxillae into a crest; thepterygoids are short, and there are thirty-two teeth in each half of each jaw.
Feresiais known from two skulls which are provided with ten to twelve teeth in each half of each jaw. It is intermediate betweenGlobicephalus,Grampus, andLagenorhynchus, according to Sir W. Flower.
The genusDelphinuscontains the Dolphin,D. delphis.[249]The genus may be characterised as follows:—Teeth small and numerous, forty-seven to sixty-five. Vertebral formula C 7, D 14 or 15, L 21 or 22, Ca 30 to 32. The atlas and axis are fused, the rest free. The palatal border of the maxillae is deeply grooved. The fins are falcate; the beak long and distinct.
The Common Dolphin of the Mediterranean shows so many variations of colour, slight differences in the proportions of the bones of the skull, and in the number of the teeth, that it has been divided up into at least seventeen "species." But M. Fischer, who has studied many of these forms, does not admit them, and most students of this group of mammals follow him in the matter. The Dolphin is and has been the most familiar of Cetaceans; in consequence it has accumulated much anecdote of a mythical character. The extreme intelligence and goodwill towards man assigned to this creature by the ancients are possibly due to the anomaly of a creature ostensibly a fish showing many of the characters of higher animals. Its unfishlike intelligence baffled the early observers, who at once endowed it with especially advanced attributes. Hence the stories of Arion and others. The leaping of the Dolphin out of the water is exemplified in many Mediterranean coins and coats of arms; the heraldic dolphin is represented with an arched back as in leaping. The Dolphin reaches a length of some 7 feet, and appears to be world-wide in range. Possibly distinct isD. longirostris, characterised, as the name denotes, by the very long beak; it has also more teeth and is a native of Malabar.D. roseiventrisagain may be a third species ofDelphinus. It comes from Torres Straits, and has the under parts rosy in colour.
The genusProdelphinushas, likeDelphinus, a distinct beak; but it has not the grooved maxillaries. No other character of importance appears to separate it fromDelphinus.
The genus consists of some eight widely distributed species, which are none of them large Dolphins.
Lagenorhynchushas the following assemblage of characters:—Head with short, not very distinct beak. Dorsal and pectoral fins falcate. Teeth small, twenty-two to forty-five in each half jaw. Vertebrae ranging in number from seventy-three to ninety-two. Pterygoid bones either in contact or separate. There are fifteen or sixteen pairs of ribs, of which six are two-headed. Of this genus Mr. True allows eight species, which have been increased by a ninth since the publication of his "Revision."[250]
Two species ofLagenorhynchusare known from our coasts; the rest are mainly southern in range. The British species are, firstly,L. albirostris, a Dolphin of some 9 feet in length. It has a large number of vertebrae, ninety-two in number.L. albirostrisis a rare species, the first record of its occurrence on these shores being in 1834. Since that date some eighteen individuals have been shot or stranded on the shores of the British Isles. The second British species,L. acutus, differs in colour from the first. As in the last, the upper parts are black and the under parts white; but inL. acutusthere is also a stripe on the flanks, brownish in colour. It has fewer vertebrae, not more than eighty-two.
The next genus of Dolphins,Sotalia, is characterised by—Teeth tolerably large, twenty-six to thirty-five. The vertebral formula is C 7, D 11 or 12, L 10 to 14, Ca 22. The pterygoids are not in contact in the middle line. It has a distinct beak.
Of this genus there are some six species (the exact number, as in so many other genera, cannot be positively asserted), most of which are fluviatile or estuarine in habit. They are also on the whole characterised by their pale, if not actually white, coloration.S. sinensisof the Amoy is white with pinkish fins.Sotalia guianensisis American as its name denotes. It is figured by van Beneden as of a pale brown colour. It is very abundant in the Bay of Rio de Janeiro, and has the reputation of being a friend of man like some other Dolphins. The natives hold that it will bring to shore the bodies of drowned persons. The most singular species of the genus is that recently described by Professor Kükenthal asS. teüszii.[251]This animal is purely fresh-water, being found inthe Camaroon river, where it is extremely rare. The nostrils (blow-hole) are prolonged into a snout-like process, a fact which is of interest in connexion with the assertion that inBalaenopterathe blow-hole is puffed out during spouting. What is temporary in the Rorqual appears to be permanent in theSotalia. More remarkable still, perhaps, is the assertion that it is a vegetable-feeding Dolphin. This is not a mere assertion except that it may not apply universally; for in the stomach of a specimen nothing but vegetable débris was found. But in the stomachs of other Whales (e.g.Rhachianectes) vegetable matter has also been found, which may perhaps have been taken in accidentally with the food.
Stenocomes nearSotalia, and Dr. Blanford has transferred to it (under the one name ofSteno perniger) the two species,Sotalia gadamuandSotalia lentiginosa. It is, however, to be distinguished fromSotaliaby the following characters:—Teeth large and few, twenty to twenty-seven on each side of each jaw, with furrowed surfaces to crowns. Vertebrae C 7, D 12 or 13, L 15, Ca 30 to 32. Pterygoids in contact. There are but two species apparently (not counting Dr. Blanford's).
Tursiopsis not a very easily definable genus. These are its chief features:—Teeth large, twenty-two to twenty-six in number in each half of each jaw. Vertebral formula C 7, D 12 or 13, L 16 or 17, Ca 27. Pterygoids in contact. Beak distinct. Some five species are allowed; but it seems to be difficult to differentiate the others fromTursiops tursio. This, the best-known form, is quite or nearly world-wide in range, and occurs, though not abundantly, on our own coasts. Mr. True has observed that the eyelids of this Whale, which is largely hunted on the American coast, are as mobile as those of a terrestrial mammal. The name "tursio" is derived from Pliny. Belon would also derive from this word the French vernacular "marsouin." The latter term is sometimes regarded as a corruption of "Meerschwein," but it would seem to be more probably derivable from "marinum suem," from the Latin direct.T. tursiohas the back black to lead-colour; the under parts white. In the reputed species,T. abusalam, from the Red Sea, the back is a dark sea-green.T. tursioreaches a length of 12 feet, but is more usually smaller.
The genusTursiomust be carefully distinguished fromTursiops. It has no dorsal fin, the teeth are small and numerous (forty-four), and the pterygoids are separate. There are two species,T. borealisandT. peronii, the former being northern and the latter more widely spread.
The genusCephalorhynchushas for its chief characters the following:—Teeth twenty-five to thirty-one, small and sharp. Pterygoids widely separated. Dorsal fin not falcate, but triangular or ovate in form. Beak not well marked off from the head. The species of this genus are all southern in range; four are perhaps to be allowed.
Fam. 3. Platanistidae.—This family of Odontocetes may be distinguished from the Dolphins by the following assemblage of structural features:—Cervical vertebrae all free, and each one of some length (for a Cetacean). Jaws long and narrow, with a considerable length of symphysis. Teeth very numerous.
This very meagre series of differential characters is largely due toPontoporiaon the Platanistid side, and toMonodonandDelphinapterusupon the Delphinid side. Otherwise the family Platanistidae would be extremely distinct. The two last-named genera have separate cervical vertebrae, and in the Beluga at any rate this is expressed externally by a quite distinct neck. Moreover, as Mr. True has pointed out, the pterygoid bones have not the involuted cavity below which characterises other Dolphins; and they have, what other Dolphins have not, an articulation outwards with the roofing bones of the skull. Sir W. Flower described the fact that in Inia (and the same occurs in Pontoporia) the palatines are separated from each other by the intervention of the vomer. In this feature they resemble certain Ziphioids,Berardius,Oulodon(=Mesoplodon)grayi, andHyperoodon. The true Dolphins also appear to show the same intervention of the vomer in a few cases. There is nothing, therefore, distinctive from the Delphinidae in this feature.
The existence of cartilaginous sternal ribs inIniaandPlatanistashows affinity between these two genera and the Physeteridae.Pontoporiais Dolphin-like in this particular, as it is also in the mode of articulation of the ribs with the vertebral column. But this last matter has already been dealt with. The principal reason for placingPontoporiawith the other two genera is the close resemblance which its skull bears to that ofInia.
The first genus of this family which will be noticed isPlatanista.The following are its main characters:—Dorsal fin absent. Eyes rudimentary. Pectoral fins large and truncated at the extremity. Teeth, about twenty-nine in each half of each jaw. Scapula with the acromion coinciding with its anterior edge. Skull with enormous maxillary crests, and with the palatines entirely concealed by the pterygoids. The length of the above definition will serve to indicate how anomalous in many particulars is the structure of this "Dolphin."
There is apparently but one species,P. gangetica, the "Susu." The Indian vernacular name is derived from the sound that the animal makes when spouting. It is an inhabitant of the Ganges and the Indus, together with their tributaries, and ascends very high up its streams. It is also thought to be purely fluviatile and never to desert the rivers for the sea.Platanistalives chiefly by grubbing in the mud for prawns and fish. Grains of rice have also been found in the stomach, but this would seem to be accidental. The long snout of the Susu has been compared to the long snout of the Gharial, a native of the same region. This Whale grows to a length of over 9 feet, but this length is exceptional. Its anatomy has been elaborately described by Dr. Anderson.[252]
The next genus,Inia, is thus to be characterised:—Dorsal fin rudimentary; pectorals large and ovate. Teeth, as many as thirty-two on each side, often with an additional tubercle. Skull without large maxillary crests; palatines not hidden by pterygoids, but divided by vomer. The vertebrae of this genus are few in number, only forty-one in all, which are thus distributed: C 7, D 13, L 3, Ca 18. The peculiarities of the vertebral column are several. In the first place, as has been mentioned in the definition of the family, all the cervicals are separate and individually of some length. Secondly, the axis has a better trace of an odontoid process than in any other Whale exceptPlatanista, where it is even more obvious. The lumbar region is remarkable on account of its restriction to three vertebrae. The sternum, by what we must regard as convergence, is somewhat like that of the Whalebone whales. It consists of one piece only, of a roughly-oval form, to which apparently only two pairs of (cartilaginous) sternal ribs are attached. In the fore-limb the proportions between the humerus and the radius are more likethose of terrestrial mammals;i.e.the humerus is distinctly the longer, the converse usually obtaining among Whales. ButPlatanistaagain agrees withInia. The teeth are remarkable for the fact that the hindermost ones of the series have an additional lobe; they are not purely conical as are those of Whales generally.
There is but one species,Inia geoffrensis, which inhabits the Amazons, and grows to a length of 8 feet. Its colour variations are rather extraordinary, unless they can be set down to sex, which has been denied. Some individuals are wholly pink; others are black above and pink beneath. This Whale is believed by the Indians to attack a man in the water, and it is added that theSotaliaof the same streams will defend him from these attacks! Naturally, therefore, superstitious reverence attaches to this Dolphin, which is tiresome to the naturalist who wants specimens, as Professor Louis Agassiz found.
In the genusPontoporia[253]the dorsal fin is well developed and falcate. The teeth are very numerous, 200 in all. The ribs articulate as in Dolphins. The skull closely resembles that of Inia, and the scapula is, as in that genus, "normal."
The proper name forPontoporiais reallyStenodelphis, which name was first used by Gervais a month or two before Gray, who separated it from the vagueDelphinusof its original discoverer, Gervais himself. It has a longer snout thanInia, which, being bent towards the extremity in a downward direction, curiously suggests the skull of a Curlew. In details, however, the skull is exceedingly like that ofInia. It is nearly symmetrical. The vertebral formula appears to be the following:—C 7, D 10, L 5, Ca 20 = 42, just one over the number of the vertebrae inInia. The sternum is in two pieces. Of the ten pairs of ribs the first three are double-headed. These and the next have sternal moieties joining the sternum, of which the first three are ossified, the last being apparently merely a ligament.
There is a single species of the genus,P. blainvillii. This Whale is described by Mr. Lydekker as being of a clear brown colour, harmonising with the waters of the estuary of the Amazons and the La Plata which it inhabits. The same colour characterisesSotalia pallidaof those parts of the world, andmay be a colour adaptation. But the extant accounts of the colour of this Dolphin vary—quite possibly in accordance with real variations, such as are exhibited byIniaalready spoken of.Pontoporia blainvilliiis a smallish Dolphin some 4 feet in length.
Fossil Odontocetes.—Several of the existing genera of Dolphins are also known in a fossil condition, as well as Ziphioid Whales closely related to existing forms. We shall deal here only with a few genera of fossil Odontocetes which depart in their structure from existing forms.
The genusPhysodonis Miocene, and has been found in Patagonia. It appears to be most nearly allied to the Physeteridae, but should probably form a distinct family.Physodonwas not so large asPhyseter, the skull measuring only some 10 feet. It thus comes nearer in point of size toKogia, and it is interesting to note that its relatively-shorter snout is also suggestive of the dwarf Cachalot. The general outline of the skull is, however, more like that ofPhyseter, and there is the same deep cavity for the lodgment of spermaceti. The main feature of interest in the skull is the presence of teeth in both jaws, and the fact that two or three are lodged in the premaxillae. This is precisely what is found in the most ancient Whales, the Zeuglodonts.
Extinct Dolphins, apparently referable to the Platanistidae, are the most numerous among the earlier forms of Cetaceans, and it is significant that the earliest known forms of these go back to the Eocene.
The genusIniopsisof Mr. Lydekker,[254]with one species,I. caucasica, comes from rocks which seem to be of that age. The back part of the skull of this animal, the only part of the skull known, has the same squarish excavation of the maxillaries that characterisesIniaandPontoporia. Its lower jaw was slender and possessed numerous teeth.
The long snout and jaws of Platanistids, especially exaggerated inPontoporiaamong living forms, are constantly found in these Tertiary Platanistids.
Eurhinodelphishad a beak three and a half times the length of the cranium, whereas inPontoporiathe proportions are as 2:1. The teeth too were very numerous.
The genusArgyrocetus, from Patagonian Tertiary strata, was an animal about as large as the existing Dolphin. It had theslender rostrum and numerous teeth of the Platanistids and the squared excavations of the maxillaries.Argyrocetus patagonicuspossessed also archaic characters, suggesting earlier affinities still. The two condyles of the skull instead of being closely adpressed to the skull stood out in a way more like that met with in terrestrial mammals. The nasal bones instead of being abbreviated rudiments are well developed as in the archaic Zeuglodonts. The cervical vertebrae of this Whale are all perfectly free from each other and individually long. The skull is on the whole bilaterally symmetrical; this again is a feature more pronounced among the Platanistidae than among other Odontocetes. Accompanying these generalised Cetacean characters are some which show that the animal was too specialised to be the direct ancestor of any existing forms. The end of the mandible was upturned and without teeth, its form being quite unique among Cetacea. Other allied forms, such asZarrhachisandPriscodelphinus, showed the same length of the cervical vertebrae.
A very distinct family of extinct Whales is that of theSqualodontidae. They to some extent bridge over the gap between the existing Odontoceti and the Eocene Archaeoceti (Zeuglodonts).
The skull of these Whales was on the whole Dolphin-like. But they possessed teeth which were distinctly specialised into incisors, canines, and molars. The molars have a coarsely-serrated cutting edge as in the Zeuglodonts, and are also to some extent two-rooted. But they are more numerous, and so far approximate to the conditions which characterise the more typical modern Odontocetes.Squalodonwas a long-beaked form, andProsqualodonhad a skull whose proportions are nearer those ofKogia.
This division of the Whale tribe embraces but a single family,Zeuglodontidae, of which but a single genus,Zeuglodon, can with certainty be discriminated.
Zeuglodonis an Eocene form of large size, with teeth which are limited in number and disposed in three series as incisors, canines, and molars. The molars are double-rooted, a fact which has given to the genus its name. The nasal bones being longinstead of rudimentary like those of other Whales, the blow-hole lies more in the middle of the face. The skull, too, is not Whale-like in a number of other points. Thus the premaxillaries take their fair share in the outline of the upper jaw; and, furthermore, bear the incisor teeth. The parietals meet above in a crest and are not excluded from the roof of the skull. The vertebrae of the neck are in no way shortened; neither are they fused together. The ribs are double-headed, and the sternum is made up of several pieces. Some naturalists, particularly Professor D'Arcy Thompson,[255]have assigned a relationship to the Seals to these ancient Cetacea; but others[256]have disputed this view chiefly on the grounds that the characters which appear to be Seal-like are simply characters which are generalised and so far at most not Whale-like. Thus the long neck and the serrated character of the teeth may be accepted as Seal-like on the one hand; but on the other, a simple serrated tooth and a long neck are not by any means features of organisation which we should consider out of the way in an ancient form of Cetacean which probably preyed upon fish. The humerus ofZeuglodon, according to Mr. Lydekker, puts out of court any possible near relationship to the Seals. But the matter under dispute can be further studied by reference to the three memoirs quoted below.
This order may be thus defined:—Small to large quadrupeds, terrestrial, arboreal, or aquatic, of usually carnivorous habits. The teeth have generally sharp and cutting edges, and the canines are well developed; the incisors are small, and four to six in number. The number of toes is never less than four. There are usually strong and sharp claws. The clavicles are incomplete or absent. In the hand the scaphoid and lunar bones are always united. The brain is well developed, and the hemispheres are well convoluted. The stomach is always simple, while the caecum, if present, is always small. The members of this group have a deciduate and zonary placenta.
The fewness of the characters used in the above definition is chiefly owing to the fact that the Seals and Sea-lions, although they are referable without a doubt to this order, have undergone in their metamorphosis into aquatic animals so many changes that some of the main features in the structure of their terrestrial relatives have been lost. This group will, however, be again characterised. We shall deal at present with the land division of the Carnivora, theCarnivora Fissipediaas they are generally termed. The name is of course given to them to distinguish them from the corresponding division of thePinnipedia. In the latter group the feet and hands are modified into "fins"; in the other the fingers and toes are cleft, as with terrestrial beasts generally.
Fig. 190.
Fig.190.—Under surface of the cranium of a Dog. × ½.apf, Anterior palatine foramen;AS, alisphenoid;as, posterior opening of alisphenoid canal;BO, basioccipital;BS, basisphenoid;cf, condylar foramen;eam, external auditory meatus;ExO, exoccipital;flm,flp, foramen lacerum medium and posterius;fm, foramen magnum;fo, foramen ovale;Fr, frontal;fr, foramen rotundum;gf, glenoid fossa;gp, post-glenoid process;Ma, malar;Mx, maxilla;oc, occipital condyle;op, optic foramen;Per, mastoid portion of periotic;pgf, post-glenoid foramen;Pl, palatine;PMx, premaxilla;pp, paroccipital process;ppf, posterior palatine foramen;PS, presphenoid;Pt, pterygoid;sf, sphenoidal fissure or foramen lacerum anterius;sm, stylomastoid foramen;SO, supraoccipital;Sq, zygomatic process of squamosal;Ty, tympanic bulla;Vo, vomer. (From Flower'sOsteology.)
A very marked feature of the terrestrial Carnivora is to be found in the structure of the teeth. The incisors are nearly always six, and are somewhat feebly developed in many cases. The canines are almost invariably very large strong teeth, and are always present. In some of the extinct Cats they reached enormous dimensions. The number of cheek teeth is not always identical; but the last premolar in the upper jaw and the first true molar in the lower jaw, known as the "carnassial" or "sectorial" teeth, mark a difference in structure between the anterior and the posterior crushing teeth; those in front of the carnassial tooth have cutting edges, and are often merely small, conical teeth; those behind have broader crowns and are tuberculate; those of simpler forms often trituberculate; those of otherswith numerous tubercles. The carnassial tooth is often, but by no means always, very much larger and especially longer than the rest of the molar and premolar series. It is less pronounced in some of the omnivorous Arctoidea. The skull of the Carnivora is longer in the more primitive types, such as the Canidae, and shorter in the more specialised Felidae. The orbit is hardly ever completely shut off by bone, though the postorbital process of the frontal sometimes approaches the corresponding upward process of the zygomatic arch. The palate, which is completely ossified, sometimes reaches back for some distance behind the teeth; it always extends as far as the last molar. The tympanic bulla is often very inflated, and if flatter, as in the Bears, is at any rate large and conspicuous. The lower jaw has a high coronoid process, and the condyle is transversely elongated, this part of the bone being rolled into an almost cylindrical form; it fits very closely into the glenoid cavity, and the articulation is thereby very strict—an obvious advantage in a creature with so great a need for power of jaw.
Fig. 191.
Fig.191.—A, Atlas of Dog. Ventral view, × ½.B, Axis of Dog. Side view, × ⅔.o, Odontoid process;pz, posterior zygapophysis;s, spinous process;sn, foramen for first spinal nerve;t, transverse process;v, vertebrarterial canal. (From Flower'sOsteology.)
In the vertebral column the atlas always has large wing-like processes; the spine of the axis vertebra has a long antero-posteriorly elongated form. The transverse processes of the fourth to the sixth cervicals are, as a rule, double. These features, however, though characteristic of the Carnivora are not by any means distinctive. The true sacrum consists of but a single vertebra to which the ilia are attached; but at most two other vertebrae are fused with this. The clavicle is always small and sometimes quite rudimentary, or even absent. The spine of the scapula is well developed, and almost equally divides thesurface of that bone. The digits of the Carnivora are mostly five, and are never less than four. The mode of progression may be digitigrade or plantigrade, and the intermediate semidigitigrade mode of walking also occurs. The brain in all Carnivora is large and well convoluted. The arrangement of the convolutions is characteristic. There are three or four gyri disposed round each other, of which the lowest surrounds the Sylvian fissure. The stomach in these creatures is always simple in form, withoutsubdivisions. The caecum is never large, and may be, as in the Bear tribe, completely absent.
Fig. 192.
Fig.192.—Brain of Dog.A, Ventral;B, dorsal;C, lateral aspect.B.ol, Olfactory lobe;Cr.ce, crura cerebri;Fi.p, great longitudinal fissure;HH,HH1, lateral lobes of cerebellum;Hyp, hypophysis;Med, spinal cord;NH, medulla oblongata;Po, pons Varolii;VH, cerebral hemispheres;Wu, middle lobe (vermis) of cerebellum;I-XII, cerebral nerves. (From Wiedersheim'sComparative Anatomy.)
The distribution of the Carnivora is world-wide, excluding only the Australian region, if, as seems probable, the Dingo of that region is an introduced species. The most striking features in their distribution are perhaps the following:—There are no Bears in the Ethiopian region or in Madagascar, and but a single species in the Neotropical. The only Carnivora in Madagascar are the Viverridae, and of the seven genera there found six are peculiar. The Procyonidae are nearly entirely New World in range; out of sixteen genera of Mustelidae only five are New World, and only two of those are peculiar to the American continent. The Hyaenidae are limited to the Old World.
The classification of the Carnivora is a matter which is difficult, and which has therefore been very variously effected. It is unfortunate that the classification of Flower (based upon the researches of H. N. Turner as well as his own, and accepted by Mivart) should fail when applied to fossil forms. For it separates with great clearness the existing genera into three great divisions, the Cynoidea, Aeluroidea, and Arctoidea, definable by visceral as well as by osteological characters. The apparent anomaly, too, of a single supposed Viverrine genus, to witBassariscus, existing in America, while all the rest of its kin are Old-World forms, was shown by his characters to be neither an anomaly nor a fact. It will be better, therefore, to divide the Carnivora into the families, Felidae, Machaerodontidae, Viverridae, Hyaenidae, Canidae, Ursidae, Procyonidae, and Mustelidae, indicating at the same time the reasons for and against retaining the three divisions of Sir W. Flower.
Fam. 1. Felidae.[258]—This family includes only the Cats (i.e.Lions, Tigers, "Cats," Hunting Leopard, etc.), and is to be distinguished by the following characters:—In the skull the auditory bulla is much inflated, and there is an internal septum; the paroccipital processes are flattened against the bullae. There is no alisphenoidal canal. The dental formula is I 3, C 1, Pm 3 to 2, M 1. The carnassial tooth of the upper jaw has three lobes to the blade; that of the lower jaw is without an inner cusp.The digits are five on the fore-feet, four on the hind. The caecum is present and small. This family contains but two genera,FelisandCynaelurus.
Fig. 193.
Fig.193.—Section of auditory bulla of Tiger.am, Auditory meatus;BO, basioccipital;e, Eustachian canal;ic,oc, two chambers of bulla divided bys, septum; *, their aperture of communication;Pt, periotic;Sq, squamosal;t, tympanic ring. (From Flower'sOsteology.)
The genusFelisis very wide in its distribution, being common to both the Old and the New Worlds. Its distinctive characters, as opposed toCynaelurus, are mainly the following:—The claws are retractile, and the retractility is more markedly developed than in the Cheetah. The molar is not so nearly in a line with the other teeth; the upper carnassial, moreover, has an inner tubercle. The legs are relatively shorter.
The complete retractility of the claws is a very distinctive feature of the true Cats. It is brought about in this way: the terminal joint of the toe, which is clad with the claw, folds back into a sheath by the outer side of or above the middle phalanx. It is held in this position by a strong ligament. The flexor muscles straighten the phalanx which bears the claw, so that the natural position for the animal is to be in a state of retracted claws, which of course preserves them from friction; when wanted for aggressive purposes, they are pulled into sight by the action of the muscles already mentioned.