The forebrain forms the bulk of the whole brain, but the large size of the hemispheres is due to the greater development of the basal and lateral portions (pedunculi cerebriandcorpora striata), while the pallium (the portion external to the lateral ventricles) is thin, and restricted to the median side of each hemisphere. As a direct result of this undoubtedly secondary reduction of the pallium—due to the excessive preponderance of the basal and lateral parts—the corpus callosum (i.e.the transverse commissure of the right and left pallium) is in birds reduced to a narrow flat bundle of a few white fibres; it is situated immediately above and behind the much stronger anterior commissure,i.e.the connexion between the corpora striata, or chief remaining part of the hemispheres. Owing to the small size of the olfactory lobes the anterior arms of the latter commissure are wanting. There is very little grey matter in the cortex of the hemispheres, the surface of which is devoid of convolutions, mostly quite smooth; in others, for instance pigeons, fowls and birds of prey, a very slight furrow might be compared with the Sylvian fissure.The Thalamencephalon is much reduced. The epiphysis, or pineal body, is quite as degenerate as in mammals, although still forming a long stalk as in reptiles. In birds, this stalk consists entirely of blood-vessels, which in the adult enclose no terminal vesicle, and fuse with the membranous linings of the skull. The midbrain is represented chiefly by the optic lobes, the cortex of which alone is homologous with thecorpora quadrageminaof the mammals. Their transverse dorsal connexion is the posterior commissure; otherwise the whole roof portion of the midbrain is reduced to a thin membrane, continuous with that which covers the Sylvian aqueduct, and this ventricle sends a lateral cavity into each optic lobe, as is the case in reptiles. The right and left lobes themselves are rent asunder (so to speak), so that they are freely visible from above, filling the corners formed by the hemispheres and the cerebellum. The latter is, in comparison with mammals; represented by its middle portion only, thevermis; in a sagittal section it shows an extremely well developedarbor vitae, produced by the transverse, repeated folding of the whole organ. In comparison with reptiles the cerebellum of birds shows high development. Forwards it covers, and has driven asunder, the optic lobes; backwards it hides the much shortened medulla oblongata.Several futile attempts have been made to draw conclusions as to the intelligence of various birds, from comparison of the weight of the whole brain with that of the body, or the weight of the hemispheres with that of other parts of the central nervous system.Thebrachial plexusis formed by four or five of the lowest cervical nerves; the last nerve of this plexus often marks the boundary of the cervical and thoracic vertebrae. The composition of the plexus varies much, not only in different species, but even individually. The most careful observations are those by Fürbringer. The serial number of these nerves depends chiefly upon the length of the neck, the extremes being represented byCypselus(10th-14th cervical) andCygnus(22nd-24th), the usual numbers of the common fowl being the 13th-17th nerves.TheCrural Plexusis divided into a crural, ischiadic and pubic portion. The first is generally composed of three nerves, the hindmost of which, thefurcalis, issues in most birds between the last two lumbo-sacral vertebrae, and then divides, one half going to the crural, the other to the sciatic portions. Theobturatoriusnerve invariably comes from the two main stems of the crural. The ischiadic portion consists generally of five or six nerves, which leave the pelvis as one thick system through the ilio-ischiadic foramen. The last nerve which contributes to the ischiadic plexus leaves the spinal column in most birds either between the two primary sacral vertebrae, or just below the hindmost of them, and sends a branch to the pubic portion which is composed of post-ischiadic nerves, partly imbedded in the kidneys, and innervates the ventral muscles between the tail and pubis, together with those of the cloaca and copulatory organs.TheSympathetic Systemforms a chain on either side of the vertebral column. In the region of the neck lateral strands pass through the transverse canal of the cervical vertebrae; but from the thoracic region onwards, where the cardiac branch to the heart is given off, each strand is double and the basal ganglia are successively connected with the next by a branch which runs ventrally over the capitulum of the rib, and by another which passes directly through the foramen or space formed between capitulum and tuberculum. In the pelvic region, from about the level of the posterior end of the ischiadic plexus, the strand of each side becomes single again, passing ventrally over the transverse processes. Lastly, towards the caudal region the right and left strands approach and anastomose, eventually coalescing in the mid line.Literature.—A. Bumm, “Das Grosshirn der Vögel,”Zeitschr. wiss. Zool., 38, 1883, pp. 430-466, pls. 24-25; F. Leuret and P. Gratiolet,Anatomie comparée du système nerveux(Paris, 1839-1857), with atlas; A. Meckel, “Anatomie des Gehirns der Vögel,” inMeckel’s Archiv f. Physiol.vol. ii.; H.F. Osborn, “The Origin of the Corpus Callosum, a contribution upon the Cerebral Commissures of the Vertebrata,”Morphol. Jahrbuch, 1886, xii. pp. 223-251, pls. 13-14; M.A. Schulgin, “Lobi optici der Vögel,”Zool. Anzeig.iv. pp. 277 and 303; E.R.A. Serres,Anatomie comparée du cerveau(Paris, 1824, 4 pls.); L. Stieda, “Studien uber das centrale Nervensystem der Vögel und Säugethiere,”Zeitschr. wiss. Zool.xix., 1869, pp. 1-92, pls.; J. Swan,Illustrations of the Comparative Anatomy of the Nervous System(London, 1835, 4to, with plates).Concerning the spinal nerves and their plexus: H. v. Jhering,Das peripherische Nervensystem der Wirbeltiere(Leipzig, 1871); W.A. Haswell, “Notes on the Anatomy of Birds,”Proc. Linn. Soc. N.S.W.iii., 1879; M. Fürbringer, “Zur Lehre von den Umbildungen der Nervenplexus,”Morph. Jahrb.v., 1879, p. 358.
The forebrain forms the bulk of the whole brain, but the large size of the hemispheres is due to the greater development of the basal and lateral portions (pedunculi cerebriandcorpora striata), while the pallium (the portion external to the lateral ventricles) is thin, and restricted to the median side of each hemisphere. As a direct result of this undoubtedly secondary reduction of the pallium—due to the excessive preponderance of the basal and lateral parts—the corpus callosum (i.e.the transverse commissure of the right and left pallium) is in birds reduced to a narrow flat bundle of a few white fibres; it is situated immediately above and behind the much stronger anterior commissure,i.e.the connexion between the corpora striata, or chief remaining part of the hemispheres. Owing to the small size of the olfactory lobes the anterior arms of the latter commissure are wanting. There is very little grey matter in the cortex of the hemispheres, the surface of which is devoid of convolutions, mostly quite smooth; in others, for instance pigeons, fowls and birds of prey, a very slight furrow might be compared with the Sylvian fissure.
The Thalamencephalon is much reduced. The epiphysis, or pineal body, is quite as degenerate as in mammals, although still forming a long stalk as in reptiles. In birds, this stalk consists entirely of blood-vessels, which in the adult enclose no terminal vesicle, and fuse with the membranous linings of the skull. The midbrain is represented chiefly by the optic lobes, the cortex of which alone is homologous with thecorpora quadrageminaof the mammals. Their transverse dorsal connexion is the posterior commissure; otherwise the whole roof portion of the midbrain is reduced to a thin membrane, continuous with that which covers the Sylvian aqueduct, and this ventricle sends a lateral cavity into each optic lobe, as is the case in reptiles. The right and left lobes themselves are rent asunder (so to speak), so that they are freely visible from above, filling the corners formed by the hemispheres and the cerebellum. The latter is, in comparison with mammals; represented by its middle portion only, thevermis; in a sagittal section it shows an extremely well developedarbor vitae, produced by the transverse, repeated folding of the whole organ. In comparison with reptiles the cerebellum of birds shows high development. Forwards it covers, and has driven asunder, the optic lobes; backwards it hides the much shortened medulla oblongata.
Several futile attempts have been made to draw conclusions as to the intelligence of various birds, from comparison of the weight of the whole brain with that of the body, or the weight of the hemispheres with that of other parts of the central nervous system.
Thebrachial plexusis formed by four or five of the lowest cervical nerves; the last nerve of this plexus often marks the boundary of the cervical and thoracic vertebrae. The composition of the plexus varies much, not only in different species, but even individually. The most careful observations are those by Fürbringer. The serial number of these nerves depends chiefly upon the length of the neck, the extremes being represented byCypselus(10th-14th cervical) andCygnus(22nd-24th), the usual numbers of the common fowl being the 13th-17th nerves.
TheCrural Plexusis divided into a crural, ischiadic and pubic portion. The first is generally composed of three nerves, the hindmost of which, thefurcalis, issues in most birds between the last two lumbo-sacral vertebrae, and then divides, one half going to the crural, the other to the sciatic portions. Theobturatoriusnerve invariably comes from the two main stems of the crural. The ischiadic portion consists generally of five or six nerves, which leave the pelvis as one thick system through the ilio-ischiadic foramen. The last nerve which contributes to the ischiadic plexus leaves the spinal column in most birds either between the two primary sacral vertebrae, or just below the hindmost of them, and sends a branch to the pubic portion which is composed of post-ischiadic nerves, partly imbedded in the kidneys, and innervates the ventral muscles between the tail and pubis, together with those of the cloaca and copulatory organs.
TheSympathetic Systemforms a chain on either side of the vertebral column. In the region of the neck lateral strands pass through the transverse canal of the cervical vertebrae; but from the thoracic region onwards, where the cardiac branch to the heart is given off, each strand is double and the basal ganglia are successively connected with the next by a branch which runs ventrally over the capitulum of the rib, and by another which passes directly through the foramen or space formed between capitulum and tuberculum. In the pelvic region, from about the level of the posterior end of the ischiadic plexus, the strand of each side becomes single again, passing ventrally over the transverse processes. Lastly, towards the caudal region the right and left strands approach and anastomose, eventually coalescing in the mid line.
Literature.—A. Bumm, “Das Grosshirn der Vögel,”Zeitschr. wiss. Zool., 38, 1883, pp. 430-466, pls. 24-25; F. Leuret and P. Gratiolet,Anatomie comparée du système nerveux(Paris, 1839-1857), with atlas; A. Meckel, “Anatomie des Gehirns der Vögel,” inMeckel’s Archiv f. Physiol.vol. ii.; H.F. Osborn, “The Origin of the Corpus Callosum, a contribution upon the Cerebral Commissures of the Vertebrata,”Morphol. Jahrbuch, 1886, xii. pp. 223-251, pls. 13-14; M.A. Schulgin, “Lobi optici der Vögel,”Zool. Anzeig.iv. pp. 277 and 303; E.R.A. Serres,Anatomie comparée du cerveau(Paris, 1824, 4 pls.); L. Stieda, “Studien uber das centrale Nervensystem der Vögel und Säugethiere,”Zeitschr. wiss. Zool.xix., 1869, pp. 1-92, pls.; J. Swan,Illustrations of the Comparative Anatomy of the Nervous System(London, 1835, 4to, with plates).
Concerning the spinal nerves and their plexus: H. v. Jhering,Das peripherische Nervensystem der Wirbeltiere(Leipzig, 1871); W.A. Haswell, “Notes on the Anatomy of Birds,”Proc. Linn. Soc. N.S.W.iii., 1879; M. Fürbringer, “Zur Lehre von den Umbildungen der Nervenplexus,”Morph. Jahrb.v., 1879, p. 358.
4.Organs of Sense.
TheEyeis essentially reptilian, but in sharpness of vision, power and quickness of accommodation it surpasses that of the mammals. The eyeball, instead of being globular, resembles rather the tube of a short and thick opera-glass.
The anterior half of the sclerotic is composed of a ring of some ten to seventeen cartilaginous or bony scales which partly overlap each other. Another cartilage or ossification, the posterior sclerotic ring, occurs within the walls of the posterior portion of the cup, and surrounds, especially in the Pici and in the Passeres, the entrance of the optic nerve. The iris is in most young birds at first brown or dull-coloured, but with maturity attains often very bright tints which add considerably to the charm of the bird; sexual dimorphism is in this respect of common occurrence. The iris contains a sphincter and a dilator muscle; the former, supplied by branches from theoculomotoriusnerve, is under control of the will, whilst the dilator fibres belong to the sympathetic system. When fully dilated, the pupil is round in all birds; when contracted it is usually round, rarely oval as in the fowl. From near the entrance of the optic nerve, through the original choroidal fissure, arises the much-folded pecten, deeply pigmented and very vascular, far into the vitreous humour. The number of its folds varies considerably, from three inCaprimulgusto nearly thirty in crow (Corvus).Apteryx, which since Owen has generally been stated to be devoid of such an organ, likewise possesses a pecten; its base is, however, trumpet-shaped, covers almost the whole of the optic disk, and extends nearly to the lens in the shape of a thick, densely pigmented cone, without any plications, resembling in these respects the pecten of many Lacertilia (see G.L. Johnson,Phil. Trans., 1901, p. 54). In the retina the cones prevail in numbers over the rods as in the mammals, and their tips contain, as in other Sauropsida, coloured drops of oil, mostly red or yellow. Near the posterior pole of the fundus, but somewhat excentrically placed towards the temporal or outer side, is thefovea centralis, a slight depression in the retina, composed almost entirely of cones, the spot of most acute vision. Many birds possess besides this temporal fovea a second fovea nearer the nasal side. It is supposed that the latter serves monocular, the other the binocular vision, most birds being able to converge their eyes upon one spot. Consequently the whole field of vision of these birds possesses three points where vision is most acute. It may here be remembered that of the mammalia man and monkeys alone are capable of convergence, and have a circumscribed macular area.Of the outer eyelids, the lower alone is movable in most birds, as in reptiles, and it frequently contains a rather large saucer-shaped cartilage, thetarsus palpebralis. The margins of the lids are sometimes furnished with eyelashes,e.g. in the ostrich and in the Amazon parrots, which are vestigial feathers without barbs. During the embryonic stage the lids are fused together, and either become separated shortly before the bird is hatched, as is the case with most Nidifugae, or else the blind condition prevails for some time, in the young Nidicolae. All birds have, like most reptiles, a well-developed third lid or “nictitating membrane,” which moves from the inner canthus obliquely upwards and backwards over the cornea. The moving mechanism is a further and much higher development of that which prevails in reptiles, there being two muscles completely separate from each other. Both are supplied by theabducensnerve, together with therectus externusmuscle. One, thequadratusorbursalismuscle, arises from the hinder surface of the eyeball, and forms with its narrow margin, which is directed towards the optic nerve, a pulley for the long tendon of thepyramidalismuscle. This arises from the nasal surface of the ball, and its tendon passes into the somewhat imperfectly transparent nictitating membrane. The quadrate muscle adjusts the motion, and prevents pressure upon the optic nerve; during the state of relaxation of both muscles the nictitans withdraws through its own elasticity.See R. Leuckart in Graefe and Saemisch’sHandbuch d. Ophthalmologie(Leipzig, 1876, vol. i. chap. 7); H. Müller,Gesammelte Schriften(Otto Becker, Leipzig, 1872), andArch. f. Ophthalmol.iii.; Ch. Rouget, “Recherches anatomiques et physiologiques sur les appareils érectiles,” “Appareil de l’adaptation de l’œil” ...Compt. Rend.(Paris, xlii., 1856, pp. 937-941); M. Schultze, art. “Retina,” in Stricker’sHandbuch der Gewebelehre, 1871, vol. ii.; J.R. Slonaker, “Comp. Study of the Area of Acute Vision in Vertebrates,”Journ. Morph., 1897.
The anterior half of the sclerotic is composed of a ring of some ten to seventeen cartilaginous or bony scales which partly overlap each other. Another cartilage or ossification, the posterior sclerotic ring, occurs within the walls of the posterior portion of the cup, and surrounds, especially in the Pici and in the Passeres, the entrance of the optic nerve. The iris is in most young birds at first brown or dull-coloured, but with maturity attains often very bright tints which add considerably to the charm of the bird; sexual dimorphism is in this respect of common occurrence. The iris contains a sphincter and a dilator muscle; the former, supplied by branches from theoculomotoriusnerve, is under control of the will, whilst the dilator fibres belong to the sympathetic system. When fully dilated, the pupil is round in all birds; when contracted it is usually round, rarely oval as in the fowl. From near the entrance of the optic nerve, through the original choroidal fissure, arises the much-folded pecten, deeply pigmented and very vascular, far into the vitreous humour. The number of its folds varies considerably, from three inCaprimulgusto nearly thirty in crow (Corvus).Apteryx, which since Owen has generally been stated to be devoid of such an organ, likewise possesses a pecten; its base is, however, trumpet-shaped, covers almost the whole of the optic disk, and extends nearly to the lens in the shape of a thick, densely pigmented cone, without any plications, resembling in these respects the pecten of many Lacertilia (see G.L. Johnson,Phil. Trans., 1901, p. 54). In the retina the cones prevail in numbers over the rods as in the mammals, and their tips contain, as in other Sauropsida, coloured drops of oil, mostly red or yellow. Near the posterior pole of the fundus, but somewhat excentrically placed towards the temporal or outer side, is thefovea centralis, a slight depression in the retina, composed almost entirely of cones, the spot of most acute vision. Many birds possess besides this temporal fovea a second fovea nearer the nasal side. It is supposed that the latter serves monocular, the other the binocular vision, most birds being able to converge their eyes upon one spot. Consequently the whole field of vision of these birds possesses three points where vision is most acute. It may here be remembered that of the mammalia man and monkeys alone are capable of convergence, and have a circumscribed macular area.
Of the outer eyelids, the lower alone is movable in most birds, as in reptiles, and it frequently contains a rather large saucer-shaped cartilage, thetarsus palpebralis. The margins of the lids are sometimes furnished with eyelashes,e.g. in the ostrich and in the Amazon parrots, which are vestigial feathers without barbs. During the embryonic stage the lids are fused together, and either become separated shortly before the bird is hatched, as is the case with most Nidifugae, or else the blind condition prevails for some time, in the young Nidicolae. All birds have, like most reptiles, a well-developed third lid or “nictitating membrane,” which moves from the inner canthus obliquely upwards and backwards over the cornea. The moving mechanism is a further and much higher development of that which prevails in reptiles, there being two muscles completely separate from each other. Both are supplied by theabducensnerve, together with therectus externusmuscle. One, thequadratusorbursalismuscle, arises from the hinder surface of the eyeball, and forms with its narrow margin, which is directed towards the optic nerve, a pulley for the long tendon of thepyramidalismuscle. This arises from the nasal surface of the ball, and its tendon passes into the somewhat imperfectly transparent nictitating membrane. The quadrate muscle adjusts the motion, and prevents pressure upon the optic nerve; during the state of relaxation of both muscles the nictitans withdraws through its own elasticity.
See R. Leuckart in Graefe and Saemisch’sHandbuch d. Ophthalmologie(Leipzig, 1876, vol. i. chap. 7); H. Müller,Gesammelte Schriften(Otto Becker, Leipzig, 1872), andArch. f. Ophthalmol.iii.; Ch. Rouget, “Recherches anatomiques et physiologiques sur les appareils érectiles,” “Appareil de l’adaptation de l’œil” ...Compt. Rend.(Paris, xlii., 1856, pp. 937-941); M. Schultze, art. “Retina,” in Stricker’sHandbuch der Gewebelehre, 1871, vol. ii.; J.R. Slonaker, “Comp. Study of the Area of Acute Vision in Vertebrates,”Journ. Morph., 1897.
Ear.—The outer opening of the ear is, with rare exceptions, concealed by feathers, which are often rather stiff, or modified into bristles. There is no other protection, but slight, imperfectly movable folds of skin arise from the outer rim. The largest ear-opening is met with in the owls, with correspondingly larger folds of skin, the function of which is less that of protection than, probably, the catching of sound. In many owls the right and left ears are asymmetrical, and this asymmetry affects the whole of the temporal region, all the bones which surround the outer and middle ear, notably the squamosal and the quadrate, so that the skull becomes lopsided, one ear being turned obliquely down, the other upwards. (For, detail see Collett,Christiania Vidensk. Forhandl., 1881, No. 3.)
The middle ear communicates with the mouth by the Eustachian tubes, which pass between the basisphenoid and basioccipital bones, and unite upon the ventral side of the sphenoid, a little behind its articulation with the pterygoids, where they open into the mouth cavity by a short membranous duct. The columellar apparatus, or auditory chain of ossicles (fig. 16), extending between the fenestra ovalis and the tympanic membrane or drum, consists of (1) the long and slender columella, a straight, ossified rod which fits with a disk into the fenestra ovalis; it is homologous with the stapes (m.st.), although not stirrup-shaped; (2) the extracolumellar mass. This is chiefly cartilaginous and sends out three processes: the dorsal (s.st.) is attached to the upper wall of the drum cavity; the outermost (e.st.) is fastened on to the middle of the drum membrane; the third, ventral or infracolumellar process (i.st.) is directed downwards and tapers out into a thin, partly cartilaginous, strand, which originally extended to the inner corner of the articular portion of the mandible, but on its long way comes to grief, being squeezed in between the pterygoid and quadrate. This long downward process being homologous with an almost exactly identical arrangement in the crocodile, and with theprocessus foliiof the mammalian malleus, it follows that the whole extracolumellar mass, that between stapes and drum, is equivalent to incus and malleus of the mammalia. There is, in birds, noannulus tympanicus. Birds possess an ear-muscle which at least acts as atensor tympani; it arises near the occipital condyle, passes through a hole into the tympanic cavity, and its tendon is, in various ways, attached to the inside of the membrane and the neighbouring extracolumellar processes.As regards the inner ear, the endolymphatic duct ends in a closedsaccus, imbedded in the dura mater of the cranial cavity. The apex of the cochlea is turned towards, and almost reaches the anterior wall of the occipital condyle; at most it makes but half a twist or turn; it possesses both Reissner’s membrane and the organ of Corti. Although thescala tympaniis so rudimentary, not reaching a higher level than in most of the reptiles, and remaining far below the mammalia, birds do not only hear extremely well, but they distinguish between and “understand” pitch, notes and melodies.See G. Breschet,Recherches anatomiques et physiologiques sur l’organe de l’audition chez les oiseaux(Paris, 1836), with Atlas; C. Hasse, various papers inZeitschr. f. wiss. Zool. vol. xvii, and inAnatomische Studien, pts. ii. and iv. (Bresku, 1871); I. Ibsen,Atlas anatomicus auris internae(Copenhagen, 1846); G. Retzius,Das Gehororgan der Wirbelthiere(Stockholm, 1884), ii. pp. 139-198, pls. 15-20.
The middle ear communicates with the mouth by the Eustachian tubes, which pass between the basisphenoid and basioccipital bones, and unite upon the ventral side of the sphenoid, a little behind its articulation with the pterygoids, where they open into the mouth cavity by a short membranous duct. The columellar apparatus, or auditory chain of ossicles (fig. 16), extending between the fenestra ovalis and the tympanic membrane or drum, consists of (1) the long and slender columella, a straight, ossified rod which fits with a disk into the fenestra ovalis; it is homologous with the stapes (m.st.), although not stirrup-shaped; (2) the extracolumellar mass. This is chiefly cartilaginous and sends out three processes: the dorsal (s.st.) is attached to the upper wall of the drum cavity; the outermost (e.st.) is fastened on to the middle of the drum membrane; the third, ventral or infracolumellar process (i.st.) is directed downwards and tapers out into a thin, partly cartilaginous, strand, which originally extended to the inner corner of the articular portion of the mandible, but on its long way comes to grief, being squeezed in between the pterygoid and quadrate. This long downward process being homologous with an almost exactly identical arrangement in the crocodile, and with theprocessus foliiof the mammalian malleus, it follows that the whole extracolumellar mass, that between stapes and drum, is equivalent to incus and malleus of the mammalia. There is, in birds, noannulus tympanicus. Birds possess an ear-muscle which at least acts as atensor tympani; it arises near the occipital condyle, passes through a hole into the tympanic cavity, and its tendon is, in various ways, attached to the inside of the membrane and the neighbouring extracolumellar processes.
As regards the inner ear, the endolymphatic duct ends in a closedsaccus, imbedded in the dura mater of the cranial cavity. The apex of the cochlea is turned towards, and almost reaches the anterior wall of the occipital condyle; at most it makes but half a twist or turn; it possesses both Reissner’s membrane and the organ of Corti. Although thescala tympaniis so rudimentary, not reaching a higher level than in most of the reptiles, and remaining far below the mammalia, birds do not only hear extremely well, but they distinguish between and “understand” pitch, notes and melodies.
See G. Breschet,Recherches anatomiques et physiologiques sur l’organe de l’audition chez les oiseaux(Paris, 1836), with Atlas; C. Hasse, various papers inZeitschr. f. wiss. Zool. vol. xvii, and inAnatomische Studien, pts. ii. and iv. (Bresku, 1871); I. Ibsen,Atlas anatomicus auris internae(Copenhagen, 1846); G. Retzius,Das Gehororgan der Wirbelthiere(Stockholm, 1884), ii. pp. 139-198, pls. 15-20.
Nose.—The olfactory organ is poorly developed, and it is still a question whether birds possess much power of smell; many are certainly devoid of it.
The olfactory perceptive membrane is restricted to the posterior innermost region of the nasal chamber, where it covers a slight bulging-out prominence on the nasal wall. This so-called third, upper or posterior conch is not a true conch, nor is that of the vestibulum; only the middle one forms a scroll, and this corresponds to the only one of reptiles and the lower of the mammals. The nasal cavity communicates with the mouth by the choanae or posterior nares, situated between the palatine process of the maxillary, the palatine and the vomer. The outer nares or nostrils are most variable in size and shape. In the Steganopodes they tend to become much reduced,e.g.in cormorants (Phalacrocoracidae), and especially inSula, where the nasal slits become completely closed up, and the greater portion of the nasal cavity is also abolished, being restricted to the olfactory region with its unusually wide choanae. The nasal septum is often more or less incomplete, producingnares peniae,e.g.in the Cathartae, in the Anseres, gulls, rails and various other aquatic birds. The secretions of the mucous membrane of the nasal cavity, and a pair of naso-lacrymal glands (not to be confounded with the Harderian and the lacrymal glands), moisten and clean the chamber. The glands are variable in size and position; when very large,e.g.in plovers, they extend upon the forehead, causing deep impressions on the bones of the skull. Jacobson’s organ has been lost by the birds, apparently without a trace in the embryonic fowl, but T.J. Parker has described vestiges of the corresponding cartilages in theApteryx(Phil. Trans., 1890).See C. Gegenbaur, “Über die Nasenmuscheln der Vögel,”Jena Zeitschr. vii., 1873, pp. 1-21.
The olfactory perceptive membrane is restricted to the posterior innermost region of the nasal chamber, where it covers a slight bulging-out prominence on the nasal wall. This so-called third, upper or posterior conch is not a true conch, nor is that of the vestibulum; only the middle one forms a scroll, and this corresponds to the only one of reptiles and the lower of the mammals. The nasal cavity communicates with the mouth by the choanae or posterior nares, situated between the palatine process of the maxillary, the palatine and the vomer. The outer nares or nostrils are most variable in size and shape. In the Steganopodes they tend to become much reduced,e.g.in cormorants (Phalacrocoracidae), and especially inSula, where the nasal slits become completely closed up, and the greater portion of the nasal cavity is also abolished, being restricted to the olfactory region with its unusually wide choanae. The nasal septum is often more or less incomplete, producingnares peniae,e.g.in the Cathartae, in the Anseres, gulls, rails and various other aquatic birds. The secretions of the mucous membrane of the nasal cavity, and a pair of naso-lacrymal glands (not to be confounded with the Harderian and the lacrymal glands), moisten and clean the chamber. The glands are variable in size and position; when very large,e.g.in plovers, they extend upon the forehead, causing deep impressions on the bones of the skull. Jacobson’s organ has been lost by the birds, apparently without a trace in the embryonic fowl, but T.J. Parker has described vestiges of the corresponding cartilages in theApteryx(Phil. Trans., 1890).
See C. Gegenbaur, “Über die Nasenmuscheln der Vögel,”Jena Zeitschr. vii., 1873, pp. 1-21.
5.Vascular System.
Theheartlies in the middle line of the body, its long axis being parallel with that of the trunk. The whole ventral surface of the pericardium is exposed when the sternum is removed. The right and left halves are completely divided by septa, no mixture of the venous and arterial blood being possible, an advance upon reptilian conditions, even the highest.
The atria are comparatively small, the walls being thin, especially those of the right, which possesses numerous muscular ridges projecting into the cavity presenting a honeycombed appearance. The interauricular septum is mostly entirely membranous; in the middle it is thinner, rather transparent, but there is no depression orfossa ovalis. The whole sinus venosus has become part of the right atrium. It receives the three great venous trunks of the body, namely thevena cava superior dextra, thevena cava superior sinistramore dorsally, and thevena cava inferiormore to the right and below; the opening of the last is guarded by two prominent valves in place of the mammalianvalvula Eustachii. The right ventricle occupies the ventral portion of the heart. The communication with the atrium is guarded by avalvula cardiaca dextra, which only in function represents the mammalian tricuspid; it consists of an oblique reduplication of the muscular fibres together with the endocardiac lining of the right ventricle, while the opposite wall is convex and forms neither a velum nor papillary muscles, norchordae tendineae. The right anterior corner of the right ventricle passes into the short stem, guarded by three semi-lunar valves, which divides into the two pulmonary arteries. There are likewise two pulmonary veins, entering the left atrium by one orifice. Two or three membranous flaps, held by numerouschordae tendineae, form a true mitral valve, and allow the blood to pass through the leftostium atrioventriculare. The blood leaves the heart past three semi-lunar valves, by therightaorta, this being alone functional, a feature characteristic of, and peculiar to, birds. Remnants of the left aortic arch persist sometimes in the shape of a ligamentous strand. The aortic trunk is very short, sends off the coronary arteries and then the leftaorta brachiocephalica, while the rest divides into the right brachiocephalic and theaorta descendens. Each brachiocephalic soon sends off its subclavian, while in the normal or more usual cases the rest proceeds as the carotid trunk, inclusive of the vertebral artery. But the carotids show several interesting modifications which have been examined chiefly by C.L. Nitzsch and by A.H. Garrod. (1) The right and left carotids converge towards the middle and extend up the neck, imbedded in a furrow along the ventral surface of the cervical vertebrae. This is the usual arrangement. (2) The two carotids are fused into onecarotis conjuncta, imbedded in a special median osseous semicanal of the vertebrae;e.g.herons, flamingos, and some parrots. (3) There is onecarotis conjuncta, but the basal portion of its original right component is obliterated, leaving a so-calledc. primaria sinistra, an unfortunate name. SuchAves laevocarotidinaeof Garrod are common,e.g.all the Passeriformes. (4) The reverse of the third modification, producing ac. primaria dextrain the bustardEupodotis. In other likewise very rare cases a left, or a left and right, superficial carotids are developed and take the place of the then vanished deep or primary carotids.Venous System.—The bird’s liver receives nearly all the blood from the stomach, gut, pancreas and spleen, as well as from the left liver itself, into the right hepatic lobe, by a right and left portal vein. Thevenae hepaticae magnaejoin thevena cava posteriorand thereby form with it thevena cava inferior. The lefthepatica magnareceives also the umbilical vein, which persists on the visceral surface of the abdominal wall, often anastomosing with the epigastric veins. A likewise unpaired venacoccygeo-mesentericais usually present. There is no renal portal system, excepting unimportant vestiges of such a system in the head kidneys.Lymphatic System.—The white blood-corpuscles are produced in the follicles at the base of the intestinal villi. The lymph vessels of the tail and hinder parts of the body enter the hypogastric veins; and at the point of junction, on either side, lies a small lymph heart, which often persists until maturity. The red blood-corpuscles are invariably oval disks, with a central nucleus which causes a slight swelling; hence they are oval and biconvex.See A.H. Garrod, “On the Carotid Arteries of Birds,”Proc. Zool. Soc., 1873, pp. 457-472; E.A. Lauth, “Mémoire sur les vaisseaux lymphatiques des oiseaux,”Ann, Sci. nat.(iii. 1824), p. 381; J.J. Mackay, “The Development of the Branchial Arterial Arches in Birds, with special reference to the Origin of the Subclavians and Carotids,”Phil. Trans.179 B (1888), pp. 111-141; L.A. Neugebauer, “Systema venosum avium,”Nov. Act. Leopold. Carol.xxi., 1844, pp. 517-698, 15 pls.; R. Gasch, “Beiträge zur vergl. Anatomic des Herzens der Vögel und Reptilien,”Arch. f. Naturgesch., 1888.
The atria are comparatively small, the walls being thin, especially those of the right, which possesses numerous muscular ridges projecting into the cavity presenting a honeycombed appearance. The interauricular septum is mostly entirely membranous; in the middle it is thinner, rather transparent, but there is no depression orfossa ovalis. The whole sinus venosus has become part of the right atrium. It receives the three great venous trunks of the body, namely thevena cava superior dextra, thevena cava superior sinistramore dorsally, and thevena cava inferiormore to the right and below; the opening of the last is guarded by two prominent valves in place of the mammalianvalvula Eustachii. The right ventricle occupies the ventral portion of the heart. The communication with the atrium is guarded by avalvula cardiaca dextra, which only in function represents the mammalian tricuspid; it consists of an oblique reduplication of the muscular fibres together with the endocardiac lining of the right ventricle, while the opposite wall is convex and forms neither a velum nor papillary muscles, norchordae tendineae. The right anterior corner of the right ventricle passes into the short stem, guarded by three semi-lunar valves, which divides into the two pulmonary arteries. There are likewise two pulmonary veins, entering the left atrium by one orifice. Two or three membranous flaps, held by numerouschordae tendineae, form a true mitral valve, and allow the blood to pass through the leftostium atrioventriculare. The blood leaves the heart past three semi-lunar valves, by therightaorta, this being alone functional, a feature characteristic of, and peculiar to, birds. Remnants of the left aortic arch persist sometimes in the shape of a ligamentous strand. The aortic trunk is very short, sends off the coronary arteries and then the leftaorta brachiocephalica, while the rest divides into the right brachiocephalic and theaorta descendens. Each brachiocephalic soon sends off its subclavian, while in the normal or more usual cases the rest proceeds as the carotid trunk, inclusive of the vertebral artery. But the carotids show several interesting modifications which have been examined chiefly by C.L. Nitzsch and by A.H. Garrod. (1) The right and left carotids converge towards the middle and extend up the neck, imbedded in a furrow along the ventral surface of the cervical vertebrae. This is the usual arrangement. (2) The two carotids are fused into onecarotis conjuncta, imbedded in a special median osseous semicanal of the vertebrae;e.g.herons, flamingos, and some parrots. (3) There is onecarotis conjuncta, but the basal portion of its original right component is obliterated, leaving a so-calledc. primaria sinistra, an unfortunate name. SuchAves laevocarotidinaeof Garrod are common,e.g.all the Passeriformes. (4) The reverse of the third modification, producing ac. primaria dextrain the bustardEupodotis. In other likewise very rare cases a left, or a left and right, superficial carotids are developed and take the place of the then vanished deep or primary carotids.
Venous System.—The bird’s liver receives nearly all the blood from the stomach, gut, pancreas and spleen, as well as from the left liver itself, into the right hepatic lobe, by a right and left portal vein. Thevenae hepaticae magnaejoin thevena cava posteriorand thereby form with it thevena cava inferior. The lefthepatica magnareceives also the umbilical vein, which persists on the visceral surface of the abdominal wall, often anastomosing with the epigastric veins. A likewise unpaired venacoccygeo-mesentericais usually present. There is no renal portal system, excepting unimportant vestiges of such a system in the head kidneys.
Lymphatic System.—The white blood-corpuscles are produced in the follicles at the base of the intestinal villi. The lymph vessels of the tail and hinder parts of the body enter the hypogastric veins; and at the point of junction, on either side, lies a small lymph heart, which often persists until maturity. The red blood-corpuscles are invariably oval disks, with a central nucleus which causes a slight swelling; hence they are oval and biconvex.
See A.H. Garrod, “On the Carotid Arteries of Birds,”Proc. Zool. Soc., 1873, pp. 457-472; E.A. Lauth, “Mémoire sur les vaisseaux lymphatiques des oiseaux,”Ann, Sci. nat.(iii. 1824), p. 381; J.J. Mackay, “The Development of the Branchial Arterial Arches in Birds, with special reference to the Origin of the Subclavians and Carotids,”Phil. Trans.179 B (1888), pp. 111-141; L.A. Neugebauer, “Systema venosum avium,”Nov. Act. Leopold. Carol.xxi., 1844, pp. 517-698, 15 pls.; R. Gasch, “Beiträge zur vergl. Anatomic des Herzens der Vögel und Reptilien,”Arch. f. Naturgesch., 1888.
6.Respiratory System.
Thelungsare small and occupy only the dorsal portion of the thoracic cavity. There is only one right and one left lobe, each traversed through its whole length by amesobronchium, whence arise about ten secondary bronchia; these send off radially arrangedparabronchia, which end blindly near the surface. The walls of these tertiary tubes send out, in all directions,canaliculi aeriferiwhich, ending in slight swellings, recall the mammalianaveoli.
Highly specialized air-sacs are characteristic of all birds. They are very thin-walled membranes, very poor in blood-vessels, formed by the bulged-out pleural or peritoneal covering of the lungs, through the parabronchial tubes of which they are filled with air. Their function is not quite clear. The usual suggestion, that the warm air contained within them assists the bird in flight, balloon-like, is absurd. They assist in the extremely rapid and vigorous ventilation of the lungs, the latter being capable of but very limited expansion and contraction in birds. Exchange of gas through the walls of the air-sacs, almost devoid of blood-vessels, can at best be much restricted.
There are five pairs of larger sacs belonging to the pulmonary system:—(1) prebronchial or cervical, extending sometimes far up the neck, even into the cranial cavities; the throat-bags of the prairie fowls (CupidoniaandPedioecetes) are a further development; (2) subbronchial or interclavicular; (3 and 4) anterior and posterior thoracic or intermediate; (5) abdominal sacs. Most of these extend through narrow apertures—foramina pneumatica—into the hollow bones, sometimes,e.g.in hornbills and screamers, into every part of the skeleton, or, in the shape of innumerable pneumatic cells, even beneath the skin. There is also a naso-pharyngeal or tympanic system of air-sacs, restricted to the head (cf. thesiphoniumdescribed in connexion with the mandible), but filling also such curious organs as the frontal excrescence ofChasmorhynchus, the Brazilian bell-bird, the throat-bag of the adjutant stork, and the gular pouch of the bustard.Thetracheaor windpipe is strengthened by numerous cartilaginous, often osseous, complete rings, but in the emeu several of these rings are incomplete in the medioventral line, and permit the inner lining of the trachea to bulge out into a large neck-pouch, which is used by both sexes as a resounding bag. In humming-birds and petrels the trachea is partly divided by a vertical, longitudinal, cartilaginous septum. In some of those birds which have a peculiarly harsh or trumpeting voice, the trachea is lengthened, forming loops which lie subcutaneously (capercally, curassow), or it enters and dilates the symphysis of the furcula (crested guineafowl); or,e.g.in the cranes and in the hooper swan, even the whole crest of the sternum becomes invaded by the much elongated, manifolded trachea.Thesyrinxor lower larynx is the most interesting and absolutely avine modification, although absent as a voice-producing organ (probably due to retrogression) in most Ratitae, storks, turkey buzzards (Cathartes) and Steganopodes. The syrinx is a modification of the lower part of the trachea and of the adjoining bronchi. Essential are vibrating membranes between the cartilaginous framework, and next, special muscles for regulating the tension. The majority of birds possess a pair of internal tympaniform membranes forming the inner or median walls of the bronchi, which are there furnished with semi-rings only. External tympaniform membranesexist, with great variations, between the specialized one or two last tracheal and some of the first bronchial rings.According to the position of the chief sound-producing membranes, three types of syrinx are distinguishable:—(1) Tracheo-bronchial, by far the commonest form, of which the two others are to a certain extent modifications. The essential feature is that the proximal end of the inner membranes is attached to the last pair of tracheal rings; outer tympaniform membranes exist generally between the 2nd, 3rd and 4th bronchial semi-rings. This type attains its highest development in the Oscines, but it occurs also in many other orders. (2) Syrinxbronchialis. The outer membranes are spread out between two or more successive bronchial semi-rings, a distance from the trachea which is, in typical cases, devoid of sounding membranes; some Cuculi, Caprimulgi, and some owls. (3) Syrinxtrachealis. The lower portion of the trachea consists of thin membranes, about half a dozen of the rings being very thin or deficient. Inner and outer membranes may exist on the bronchi. TheTracheophonaeamong the Passeriformes, the possessors of this specialized although low type of syrinx, form a tolerably well-marked group, entirely neotropical. But indications of such a syrinx occur also inPittidae, pigeons and gallinaceous birds (Gallidae), the last cases being clearly analogous.Whilst the type of syrinx affords no help in classification, it is very different with its muscles. These—as indicated by their supply from a branch of the hypoglossal nerve, which descends on either side of the trachea—are, so to speak, a detached, now mostly independent colony of glosso-pharyngeal muscles. Omitting the paired tracheo-clavicular muscles, we restrict ourselves to the syringeal proper, those which extend between tracheal and bronchial rings. Their numbers vary from one pair to seven, and they are inserted either upon the middle portion of the bronchial semi-rings (Mesomyodi), or upon the ends of these semi-rings where these pass into the inner tympaniform membrane (Acromyodi). The former is morphologically the more primitive condition, and is found in the overwhelming majority of birds, including many Passeriformes. The acromyodian type is restricted almost entirely to the Oscines. Further, according to these muscles being inserted only upon the dorsal, or only upon the ventral, or on both ends of the semi-rings, we distinguish betweenan-,kat- anddiacromyodi. But the distinction between suchAcromyodiand theMesomyodiis not always safe. For instance, theTyranninaeare anacromyod, while the closely allied Pipras and Cotingas are katacromyod; both these modifications can be shown to have been derived but recently from the weak meso- and oligomyodian condition which prevails in the majority of the so-calledOligomyodi. On the other hand, the diacromyodian type can have been developed only from a strong muscular basis which could split into a dorsal and a ventral mass; moreover, no Passeres are known to be intermediate between those that are diacromyodian and those that are not.Attempts to derive the anacromyodian and the katacromyodian from the diacromyodian condition are easy on paper, but quite hopeless when hampered by the knowledge of anatomical facts and how to use them. There remains but one logical way, namely, to distinguish as follows:—(1)Passeres anisomyodi, in which the syrinx muscles are unequally inserted, either on the middle or on one end of the semi-rings, either dorsal or ventral. This type comprises the Clamatores. (2)Passeres diacromyodi, in which some of the syrinx muscles are attached to the dorsal, and some to the ventral ends, those ends being, so to say, equally treated. This type comprises the Oscines. Both types represent rather two divergent lines than successive stages, although that of the Clamatores remains at a lower level, possessing at the utmost three pairs of muscles, whilst these range in the Oscines from rarely two or three to five or seven.This way of using the characters of the syrinx for the classification of the Passeriformes seems simple, but it took a long time to accomplish. Joh. Müller introduced the termsPolymyodiandTracheaphones, Huxley that ofOligomyodi; Müller himself had, moreover, pointed out the more important characters of the mode of insertion, but it was Garrod who invented the corresponding terms ofAcro- andMesomyodi(=Tracheophones+Oligomyodi). (For further historical detail, seeOrnithology). After W.A. Forbes had investigated such important genera asPhilepittaandXenicus, P.L. Sclater, A. Newton and R.B. Sharpe divided the Passeres respectively intoOscines, Oligomyodae, TracheophonaeandPseudoscines(=Suboscines);Oligomyodae, TracheophonaeandAcromyodae; Oscines, Oligomyodae, TracheophonaeandAtrichiidae. Ignoring the fact that someOligomyodaeare meso- and others acromyodian, they tried to combine two irreconcilable principles, namely, mere numbers against quality.Bibliography.—M. Baer, “Beitr. z. Kenntniss d. Atemwerkzeuge bei den Vögeln,”Zeitschr. wiss. Zool. lxi. 1896, pp. 420-498; Campana,Physiologie de la respiration chez les oiseaux. Anatomie de l’appareil pneumatique... (Paris, 1875); A.H. Garrod, “Major Divisions of Passerine Birds (syrinx, &c.),”P.Z.S., 1876, pp. 506-519; and “On the Conformation of the Thoracic Extremity of the Trachea in the ClassAves,”P.Z.S., 1879, pp. 357-380; J. Müller,Stimmorgane der Passerinen, Müller’s Arch. (1847); andAbh. Akad. Wiss. (Berlin, 1845-1847), translation by F.J. Bell, Oxford, 1878; H. Strasser, “Luftsäcke der Vögel,”Morph. Jahrb. iii., 1877, pp. 179-227; C. Wunderlich, “Unterer Kehlkopf der Vögel,”Nov. Act. Leop. Carol., 1884; Ph. C. Sappey,Recherches sur l’appareil respiratoire des oiseaux(Paris, 1847); W.A. Forbes, “Contributions to the Anatomy of Passerine Birds (syrinx),”P.Z.S., 1880, pp. 380-386, 387-391; 1881, pp. 435-737; 1882, pp. 544-546, 569-571; W. Yarrell, “Observations on the tracheae of Birds,”Trans. Linn. Soc., 1827, pp. 378-391.
There are five pairs of larger sacs belonging to the pulmonary system:—(1) prebronchial or cervical, extending sometimes far up the neck, even into the cranial cavities; the throat-bags of the prairie fowls (CupidoniaandPedioecetes) are a further development; (2) subbronchial or interclavicular; (3 and 4) anterior and posterior thoracic or intermediate; (5) abdominal sacs. Most of these extend through narrow apertures—foramina pneumatica—into the hollow bones, sometimes,e.g.in hornbills and screamers, into every part of the skeleton, or, in the shape of innumerable pneumatic cells, even beneath the skin. There is also a naso-pharyngeal or tympanic system of air-sacs, restricted to the head (cf. thesiphoniumdescribed in connexion with the mandible), but filling also such curious organs as the frontal excrescence ofChasmorhynchus, the Brazilian bell-bird, the throat-bag of the adjutant stork, and the gular pouch of the bustard.
Thetracheaor windpipe is strengthened by numerous cartilaginous, often osseous, complete rings, but in the emeu several of these rings are incomplete in the medioventral line, and permit the inner lining of the trachea to bulge out into a large neck-pouch, which is used by both sexes as a resounding bag. In humming-birds and petrels the trachea is partly divided by a vertical, longitudinal, cartilaginous septum. In some of those birds which have a peculiarly harsh or trumpeting voice, the trachea is lengthened, forming loops which lie subcutaneously (capercally, curassow), or it enters and dilates the symphysis of the furcula (crested guineafowl); or,e.g.in the cranes and in the hooper swan, even the whole crest of the sternum becomes invaded by the much elongated, manifolded trachea.
Thesyrinxor lower larynx is the most interesting and absolutely avine modification, although absent as a voice-producing organ (probably due to retrogression) in most Ratitae, storks, turkey buzzards (Cathartes) and Steganopodes. The syrinx is a modification of the lower part of the trachea and of the adjoining bronchi. Essential are vibrating membranes between the cartilaginous framework, and next, special muscles for regulating the tension. The majority of birds possess a pair of internal tympaniform membranes forming the inner or median walls of the bronchi, which are there furnished with semi-rings only. External tympaniform membranesexist, with great variations, between the specialized one or two last tracheal and some of the first bronchial rings.
According to the position of the chief sound-producing membranes, three types of syrinx are distinguishable:—(1) Tracheo-bronchial, by far the commonest form, of which the two others are to a certain extent modifications. The essential feature is that the proximal end of the inner membranes is attached to the last pair of tracheal rings; outer tympaniform membranes exist generally between the 2nd, 3rd and 4th bronchial semi-rings. This type attains its highest development in the Oscines, but it occurs also in many other orders. (2) Syrinxbronchialis. The outer membranes are spread out between two or more successive bronchial semi-rings, a distance from the trachea which is, in typical cases, devoid of sounding membranes; some Cuculi, Caprimulgi, and some owls. (3) Syrinxtrachealis. The lower portion of the trachea consists of thin membranes, about half a dozen of the rings being very thin or deficient. Inner and outer membranes may exist on the bronchi. TheTracheophonaeamong the Passeriformes, the possessors of this specialized although low type of syrinx, form a tolerably well-marked group, entirely neotropical. But indications of such a syrinx occur also inPittidae, pigeons and gallinaceous birds (Gallidae), the last cases being clearly analogous.
Whilst the type of syrinx affords no help in classification, it is very different with its muscles. These—as indicated by their supply from a branch of the hypoglossal nerve, which descends on either side of the trachea—are, so to speak, a detached, now mostly independent colony of glosso-pharyngeal muscles. Omitting the paired tracheo-clavicular muscles, we restrict ourselves to the syringeal proper, those which extend between tracheal and bronchial rings. Their numbers vary from one pair to seven, and they are inserted either upon the middle portion of the bronchial semi-rings (Mesomyodi), or upon the ends of these semi-rings where these pass into the inner tympaniform membrane (Acromyodi). The former is morphologically the more primitive condition, and is found in the overwhelming majority of birds, including many Passeriformes. The acromyodian type is restricted almost entirely to the Oscines. Further, according to these muscles being inserted only upon the dorsal, or only upon the ventral, or on both ends of the semi-rings, we distinguish betweenan-,kat- anddiacromyodi. But the distinction between suchAcromyodiand theMesomyodiis not always safe. For instance, theTyranninaeare anacromyod, while the closely allied Pipras and Cotingas are katacromyod; both these modifications can be shown to have been derived but recently from the weak meso- and oligomyodian condition which prevails in the majority of the so-calledOligomyodi. On the other hand, the diacromyodian type can have been developed only from a strong muscular basis which could split into a dorsal and a ventral mass; moreover, no Passeres are known to be intermediate between those that are diacromyodian and those that are not.
Attempts to derive the anacromyodian and the katacromyodian from the diacromyodian condition are easy on paper, but quite hopeless when hampered by the knowledge of anatomical facts and how to use them. There remains but one logical way, namely, to distinguish as follows:—(1)Passeres anisomyodi, in which the syrinx muscles are unequally inserted, either on the middle or on one end of the semi-rings, either dorsal or ventral. This type comprises the Clamatores. (2)Passeres diacromyodi, in which some of the syrinx muscles are attached to the dorsal, and some to the ventral ends, those ends being, so to say, equally treated. This type comprises the Oscines. Both types represent rather two divergent lines than successive stages, although that of the Clamatores remains at a lower level, possessing at the utmost three pairs of muscles, whilst these range in the Oscines from rarely two or three to five or seven.
This way of using the characters of the syrinx for the classification of the Passeriformes seems simple, but it took a long time to accomplish. Joh. Müller introduced the termsPolymyodiandTracheaphones, Huxley that ofOligomyodi; Müller himself had, moreover, pointed out the more important characters of the mode of insertion, but it was Garrod who invented the corresponding terms ofAcro- andMesomyodi(=Tracheophones+Oligomyodi). (For further historical detail, seeOrnithology). After W.A. Forbes had investigated such important genera asPhilepittaandXenicus, P.L. Sclater, A. Newton and R.B. Sharpe divided the Passeres respectively intoOscines, Oligomyodae, TracheophonaeandPseudoscines(=Suboscines);Oligomyodae, TracheophonaeandAcromyodae; Oscines, Oligomyodae, TracheophonaeandAtrichiidae. Ignoring the fact that someOligomyodaeare meso- and others acromyodian, they tried to combine two irreconcilable principles, namely, mere numbers against quality.
Bibliography.—M. Baer, “Beitr. z. Kenntniss d. Atemwerkzeuge bei den Vögeln,”Zeitschr. wiss. Zool. lxi. 1896, pp. 420-498; Campana,Physiologie de la respiration chez les oiseaux. Anatomie de l’appareil pneumatique... (Paris, 1875); A.H. Garrod, “Major Divisions of Passerine Birds (syrinx, &c.),”P.Z.S., 1876, pp. 506-519; and “On the Conformation of the Thoracic Extremity of the Trachea in the ClassAves,”P.Z.S., 1879, pp. 357-380; J. Müller,Stimmorgane der Passerinen, Müller’s Arch. (1847); andAbh. Akad. Wiss. (Berlin, 1845-1847), translation by F.J. Bell, Oxford, 1878; H. Strasser, “Luftsäcke der Vögel,”Morph. Jahrb. iii., 1877, pp. 179-227; C. Wunderlich, “Unterer Kehlkopf der Vögel,”Nov. Act. Leop. Carol., 1884; Ph. C. Sappey,Recherches sur l’appareil respiratoire des oiseaux(Paris, 1847); W.A. Forbes, “Contributions to the Anatomy of Passerine Birds (syrinx),”P.Z.S., 1880, pp. 380-386, 387-391; 1881, pp. 435-737; 1882, pp. 544-546, 569-571; W. Yarrell, “Observations on the tracheae of Birds,”Trans. Linn. Soc., 1827, pp. 378-391.
7.Digestive System.
For a general account of the digestive organs, seeAlimentary Canal. Here only a few peculiar features may be mentioned.
The young pigeons are fed by both parents with a peculiar stuff, the product of the strongly proliferating epithelial cells of the crop, which cells undergo a cheese-like fatty degeneration, and mixed with mucus, perhaps also with the proventricular juice, make up a milk-like fluid. Should the young die or be removed during this period, the parents are liable to die, suffering severely from the turgid congestion of the hypertrophied walls of the crop.The male of the hornbills,Bucerotinae, feeds his mate, which is imprisoned, or walled-up in a hollow tree, during the whole time of incubation, by regorging his food. This bolus is surrounded, as by a bag, by the cast-up lining of the gizzard. Since this process is repeated for many days the habitual reaction of the stomach well-nigh exhausts the male. A graphic account of this is given in Livingstone’s travels.The hoactzin,Opisthocomus, feeds to a great extent upon the leaves of the aroidMontrichardiaorCaladium arborescens. The crop is modified into a large and very rugose triturating apparatus, while the gizzard, thereby relieved of its function, is reduced to the utmost. The large and heavy crop has caused a unique modification of the sternal apparatus. The keel is pushed back to the distal third of the sternum, whilst the original anterior margin of the keel is correspondingly elongated, and the furcula fused with the rostral portion.In the ostrich,Struthio, the craze of overloading the stomach with pebbles which, when triturated into sand, are not voided, has brought about a dislocation, so that the enormously widened and stretched space between proventriculus and gizzard forms a bag, directed downwards, whilst the gizzard itself with part of the duodenum is rotated round its axis to more than 100°. A similar rotation and dislocation occurs in various petrels, in correlation with the indigestible sepia-bills, &c., which these birds swallow in great quantities. InPlotus, the snakebird, the pyloric chamber of the stomach is beset with a mass of hair-like stiff filaments which permit nothing but fluid to pass into the duodenum. The gizzard of various birds which are addicted to eating hairy caterpillars,e.g.Cuculus canorusand trogons, is often lined with the broken-off hairs of these caterpillars, which, penetrating the cuticle, assume a regular spiral arrangement, due to the rotatory motion of the muscles of the gizzard.8.Cloaca and Genital Organs.The cloaca is divided by transverse circular folds, which project from its inner walls, into three successive chambers. The innermost, the coprodaeum, is an oval dilatation of the end of the rectum, and attains its greatest size in those birds whose faeces are very fluid; it serves entirely as the temporary receptacle of the faeces and the urine. The next chamber, the urodaeum, is small, and receives in its dorso-lateral wall the ureters and the genital ducts; above and below this chamber is closed by circular folds, the lower of which, towards the ventral side, passes into the coating of the copulatory organ when such is present. The urodaeum serves only as a passage, the urine being mixed with the faeces in the chamber above. The third or outermost chamber, the proctodaeum, is closed externally by the sphincter ani; the orifice is quite circular. It lodges the copulatory organ, and on its dorsal wall lies thebursa Fabricii, an organ peculiar to birds. It is most developed in the young of both sexes, is of unknown function, and becomes more or less obliterated in the adult. Only in the ostrich it remains throughout life, being specialized into a large receptacle for the urine, an absolutely unique arrangement. A true urinary bladder,i.e. a ventral dilatation of the urodaeum, is absent in all birds. It is significant that the whole type of their cloaca much resembles that of the Crocodilia and Chelonia, in opposition to that of the Lacertilia.The penis, and its much reduced vestige of the female, is developed from the ventral wall of the proctodaeum. It occurs in two different forms. In the Ratitae, exceptRhea, it consists mainly of a right and left united half (corpora fibrosa), with a deep longitudinal furrow on the dorsal side, and much resembles the same organ in crocodiles and tortoises. It is protruded and retracted by special muscles which are partly attached to the ventral, distal end of the ilium. Another type exists inRheaand in theAnseriformes, greatly specialized by being spirally twisted and partly reversible like the finger of a glove. This is mainly due to the greater development of an unpaired, median portion, analogous to the mammaliancorpus spongiosum, which is much less prominent in the Ratitae; the muscles of this type are derived solely from the anal sphincter. In other Carinatae,e.g. tinamous and storks, the penis is very much smaller and simpler, with every appearance of a degenerated organ. In the great majority of birds it has disappeared completely and the primitive way of everting the cloaca is resorted to.Both right and left testes are functional. They become greatlyenlarged in the breeding season; in the sparrow, for instance, from the size of a mustard seed to that of a small cherry. The vas deferens descends with many undulations down the lateral side of the ureter of the same side, and opens upon a small papilla into the urodaeum. Extraordinary increase in length during the breeding season causes the vasa deferentia in some of the African weaver-birds to protrude, or to bulge out the cloacal walls beyond the vent. The spermatozoa exhibit many differences in shape, size and proportions, in the various groups of birds. They have been studied minutely by E. Ballowitz.Only the left ovary becomes functional, with rare individual exceptions. Both present the appearance of diminutive clusters of grapes, at the anterior end of the kidneys, close to the suprarenal bodies, separated from each other by the descending aorta and by the vena cava where this is formed by the right and leftvena iliaca communis. During the breeding season many more eggs are developed than reach maturity, amounting in most birds to several dozens. Those germs which do not ripen during the season undergo a process of resorption, and in the winter the whole ovary dwindles to often a diminutive size. In young birds both oviducts are almost equal in size, but the right soon degenerates into an insignificant strand. During every laying season the left duct increases enormously by new formation of its component fibres. For instance, in the fowl its volume increases about fifty-fold, growing from some 6 in. in length and scarcely one line in width to more than 2 ft. in length and ½ in. in thickness. The upper, wide opening of the duct is attached by elastic, peritoneal lamellae to the hinder margin of the left lung; the middle portion of the duct is glandular and thick-walled, for the deposition of the albumen; it is connected by a short, constricted “isthmus” (where the shell-membrane is formed) with a dilated “uterus” in which the egg receives its calcareous shell and eventual pigmentation.Bibliography.—A. v. Brunn,Rückbildung nicht ausgestossener Eierstockseier, Henle Festschrift(Bonn, 1882); E. Ballowitz, “Die Spermatozoen der Vögel,”Arch. Mikr. Anat.xxxii., 1888, pls. 14-18; M. Sacchi, “Contribuzione all’ istiologia del ovidotto dei saurop-sidi,”Att. Soc. Ital., Milano, vol. xxx.; W.A. Forbes, “On the Bursa Fabricii in Birds,”P.Z.S., 1877, pp. 304-318; H. Gadow, “Remarks on the Cloaca and on the Copulatory Organs of the Amniota.”Phil. Trans., 1887, pp. 5-37, pls. 2-5; Martin Saint Ange, “Étude de l’appareil reproducteur dans les cinq classes d’animaux vertébres,”Mem. Ac. Soc., Paris, xiv., 1856; E. Retterer, “Contribution à l’étude du cloaque et de la bourse de Fabricius,”Robin’s Journ. de l’anat. et physiol., 1885, pp. 369-454, pls. 17-19.
The young pigeons are fed by both parents with a peculiar stuff, the product of the strongly proliferating epithelial cells of the crop, which cells undergo a cheese-like fatty degeneration, and mixed with mucus, perhaps also with the proventricular juice, make up a milk-like fluid. Should the young die or be removed during this period, the parents are liable to die, suffering severely from the turgid congestion of the hypertrophied walls of the crop.
The male of the hornbills,Bucerotinae, feeds his mate, which is imprisoned, or walled-up in a hollow tree, during the whole time of incubation, by regorging his food. This bolus is surrounded, as by a bag, by the cast-up lining of the gizzard. Since this process is repeated for many days the habitual reaction of the stomach well-nigh exhausts the male. A graphic account of this is given in Livingstone’s travels.
The hoactzin,Opisthocomus, feeds to a great extent upon the leaves of the aroidMontrichardiaorCaladium arborescens. The crop is modified into a large and very rugose triturating apparatus, while the gizzard, thereby relieved of its function, is reduced to the utmost. The large and heavy crop has caused a unique modification of the sternal apparatus. The keel is pushed back to the distal third of the sternum, whilst the original anterior margin of the keel is correspondingly elongated, and the furcula fused with the rostral portion.
In the ostrich,Struthio, the craze of overloading the stomach with pebbles which, when triturated into sand, are not voided, has brought about a dislocation, so that the enormously widened and stretched space between proventriculus and gizzard forms a bag, directed downwards, whilst the gizzard itself with part of the duodenum is rotated round its axis to more than 100°. A similar rotation and dislocation occurs in various petrels, in correlation with the indigestible sepia-bills, &c., which these birds swallow in great quantities. InPlotus, the snakebird, the pyloric chamber of the stomach is beset with a mass of hair-like stiff filaments which permit nothing but fluid to pass into the duodenum. The gizzard of various birds which are addicted to eating hairy caterpillars,e.g.Cuculus canorusand trogons, is often lined with the broken-off hairs of these caterpillars, which, penetrating the cuticle, assume a regular spiral arrangement, due to the rotatory motion of the muscles of the gizzard.
8.Cloaca and Genital Organs.
The cloaca is divided by transverse circular folds, which project from its inner walls, into three successive chambers. The innermost, the coprodaeum, is an oval dilatation of the end of the rectum, and attains its greatest size in those birds whose faeces are very fluid; it serves entirely as the temporary receptacle of the faeces and the urine. The next chamber, the urodaeum, is small, and receives in its dorso-lateral wall the ureters and the genital ducts; above and below this chamber is closed by circular folds, the lower of which, towards the ventral side, passes into the coating of the copulatory organ when such is present. The urodaeum serves only as a passage, the urine being mixed with the faeces in the chamber above. The third or outermost chamber, the proctodaeum, is closed externally by the sphincter ani; the orifice is quite circular. It lodges the copulatory organ, and on its dorsal wall lies thebursa Fabricii, an organ peculiar to birds. It is most developed in the young of both sexes, is of unknown function, and becomes more or less obliterated in the adult. Only in the ostrich it remains throughout life, being specialized into a large receptacle for the urine, an absolutely unique arrangement. A true urinary bladder,i.e. a ventral dilatation of the urodaeum, is absent in all birds. It is significant that the whole type of their cloaca much resembles that of the Crocodilia and Chelonia, in opposition to that of the Lacertilia.
The penis, and its much reduced vestige of the female, is developed from the ventral wall of the proctodaeum. It occurs in two different forms. In the Ratitae, exceptRhea, it consists mainly of a right and left united half (corpora fibrosa), with a deep longitudinal furrow on the dorsal side, and much resembles the same organ in crocodiles and tortoises. It is protruded and retracted by special muscles which are partly attached to the ventral, distal end of the ilium. Another type exists inRheaand in theAnseriformes, greatly specialized by being spirally twisted and partly reversible like the finger of a glove. This is mainly due to the greater development of an unpaired, median portion, analogous to the mammaliancorpus spongiosum, which is much less prominent in the Ratitae; the muscles of this type are derived solely from the anal sphincter. In other Carinatae,e.g. tinamous and storks, the penis is very much smaller and simpler, with every appearance of a degenerated organ. In the great majority of birds it has disappeared completely and the primitive way of everting the cloaca is resorted to.
Both right and left testes are functional. They become greatlyenlarged in the breeding season; in the sparrow, for instance, from the size of a mustard seed to that of a small cherry. The vas deferens descends with many undulations down the lateral side of the ureter of the same side, and opens upon a small papilla into the urodaeum. Extraordinary increase in length during the breeding season causes the vasa deferentia in some of the African weaver-birds to protrude, or to bulge out the cloacal walls beyond the vent. The spermatozoa exhibit many differences in shape, size and proportions, in the various groups of birds. They have been studied minutely by E. Ballowitz.
Only the left ovary becomes functional, with rare individual exceptions. Both present the appearance of diminutive clusters of grapes, at the anterior end of the kidneys, close to the suprarenal bodies, separated from each other by the descending aorta and by the vena cava where this is formed by the right and leftvena iliaca communis. During the breeding season many more eggs are developed than reach maturity, amounting in most birds to several dozens. Those germs which do not ripen during the season undergo a process of resorption, and in the winter the whole ovary dwindles to often a diminutive size. In young birds both oviducts are almost equal in size, but the right soon degenerates into an insignificant strand. During every laying season the left duct increases enormously by new formation of its component fibres. For instance, in the fowl its volume increases about fifty-fold, growing from some 6 in. in length and scarcely one line in width to more than 2 ft. in length and ½ in. in thickness. The upper, wide opening of the duct is attached by elastic, peritoneal lamellae to the hinder margin of the left lung; the middle portion of the duct is glandular and thick-walled, for the deposition of the albumen; it is connected by a short, constricted “isthmus” (where the shell-membrane is formed) with a dilated “uterus” in which the egg receives its calcareous shell and eventual pigmentation.
Bibliography.—A. v. Brunn,Rückbildung nicht ausgestossener Eierstockseier, Henle Festschrift(Bonn, 1882); E. Ballowitz, “Die Spermatozoen der Vögel,”Arch. Mikr. Anat.xxxii., 1888, pls. 14-18; M. Sacchi, “Contribuzione all’ istiologia del ovidotto dei saurop-sidi,”Att. Soc. Ital., Milano, vol. xxx.; W.A. Forbes, “On the Bursa Fabricii in Birds,”P.Z.S., 1877, pp. 304-318; H. Gadow, “Remarks on the Cloaca and on the Copulatory Organs of the Amniota.”Phil. Trans., 1887, pp. 5-37, pls. 2-5; Martin Saint Ange, “Étude de l’appareil reproducteur dans les cinq classes d’animaux vertébres,”Mem. Ac. Soc., Paris, xiv., 1856; E. Retterer, “Contribution à l’étude du cloaque et de la bourse de Fabricius,”Robin’s Journ. de l’anat. et physiol., 1885, pp. 369-454, pls. 17-19.
B. Fossil Birds
Much had naturally been expected from the study of fossil birds, but, so far as the making of classifications is concerned, they have proved rather a source of perplexities. So long as the characters of new fossils are only of specific and generic value, it is mostly possible to assign the birds to their proper place, but when these characters indicate new families or orders, for instance Hesperornithes, Ichthyornithes, Palaelodi, their owners are put outside the more tersely constructed classifications applicable to modern birds. It is no exaggeration to say that the genus, often even the species, can be determined from almost any recent bone, but in the case of Miocene, and still more, of Eocene fossils, we have often to deal with strange families, which either represent an extinct side branch, or which connect several recent groups with each other. Our artificially-established classifications collapse whilst we gain further insight into the mutual affinities of the existing groups. Of course this must be so if evolution is true. But it also follows that, if every extinct and recent bird were known, neither species, nor genera, nor families, nor orders could be defined. We should be able to construct the pedigree of every group, in other words, the gigantic natural system, but there would be no classification. Much light has also been thrown by fossil birds upon the study of geographical distribution. The key to the distribution of recent groups lies in that of the extinct forms. Not only have many absolutely new families been discovered, but many kinds of modern birds are now known to have existed also in countries which they are now extinct. There were, for instance, trogons, secretary-birds, parrots, and other now Ethiopian forms in Miocene France. Ostriches, undistinguishable fromStruthio, have been found in Samos and in the Sivalik Hills.
The proper study of fossil birds may be said to have begun with A. Milne-Edwards, whose magnificentOiseaux fossiles de la Francewas published from 1867 to 1871. This work deals chiefly with mid-Tertiary forms. A new impetus was given by O.C. Marsh, who, after 1870, discovered a great number of bird remains in the Cretaceous strata of North America. The most important result is the proof that, until the end of the Cretaceous epoch, most, if not all, birds were still possessed of teeth (seeOdontornithes).
The oldest known bird is theArchaeopteryx(q.v.), of the upper Oolite in Bavaria. The imprints in the enormously older new red sandstone or Lower Trias of Connecticut, and originally namedOrnithichnites, belong to Dinosaurian Reptiles.
A wide gap separatesArchaeopteryxfrom the next order of fossil birds of the Cretaceous epoch, and, since freshwater deposits of that age are rare, bird remains are uncommon. Many bones formerly referred to birds have since proved to belong to Pterodactyls,e.g.Cimoliornisfrom the English Chalk. But in 1858 were discerned in the Upper Greensand of Cambridgeshire remains which are now known asEnaliornis. W. Dames has described bones from the Chalk of southern Sweden under the name ofScaniornis, probably allied toPalaelodus. From the Cretaceous rocks of North America a large number of birds have been described by O.C. Marsh. Of these the most interesting areIchthyornis(=Graculavus) andHesperornis, from the Cretaceous shales of Kansas. They were placed by Marsh in a distinct subclass of birds,Odontornithes(q.v.). Probably all birds of Cretaceous age were still possessed of teeth.Baptornis, another of Marsh’s genera, seems to be allied toEnaliornis,PalaeotringaandTalmatornis, were by him referred to Limicoline and Passerine birds.Laornisfrom the Cretaceous marls of New Jersey was as large as a swan.
The lower Eocene has furnished a greater number of bird bones. Some of the largest are those ofGastornis, with three species from France, Belgium and England. Much difference of opinion obtains as to the affinities of these birds, which were far larger than an ostrich; they were undoubtedly incapable of flight and there are indications of teeth in the upper jaw. Provisionally this genus has been grouped with the Ratitae, which at any rate are a heterogenous assembly. Sir R. Owen’sDasornis, of the London Clay, known from an imperfect cranium, and E.D. Cope’sDiatrymaof New Mexico, based upon a gigantic metatarsus, may also belong there. The London Clay of South England has likewise supplied some long upper arm bones,Argillornis. The most remarkable specimen is a skull,Odontopteryx toliapicus(figs. 17, 18); the edges of the jaws were serrated like those of certain tortoises. The character of this skull and the compound rhamphotheca (known by the imprints left upon the jaws) indicate affinities with the Steganopodes. Remnantsof a heron-like bird,Proherodius, of a gull-like creature,Halcyornis, a raptorialLithornis; and a supposed Passerine from Glarus in Switzerland, calledProtornis = Osteornis, complete the list.
The upper Eocene has yielded many birds, most of which are at least close forerunners of recent genera, the differentiation into the leading orders and families being already well marked,e.g.Gallinaceous birds, stork- and crane-like waders, rails, birds of prey, cormorants, &c. Especially numerous bones have been found in the Paris basin, chiefly described by G. Cuvier, F.L.P. Gervais, E. Blanchard, and above all by A. Milne-Edwards, and in the equivalent beds of Hampshire. Others have been discovered in Wyoming; a giant penguin,Palaecudyptes, is known from New Zealand, andPalaeospheniscusfrom Patagonia. The Miocene has yielded by far the greatest number of bird-bones, including even eggs and imprints of feathers. For instance, from the lower Miocene beds of Allier and Puy-de-Dôme Milne-Edwards has described about 50 species. Of thesePalaeloduswas an ancestral flamingo, but with shorter legs;Limnatornisis referred to the hoopoes. The existing genera includeAnas, Aquila, Bubo, Columba, Cypselus, Lanius, Picus, Phalacrocorax, Sula, &c.Very interesting is the fact thatSerpentarius, PsittacusandTrogonare amongst this list of birds, which are now restricted to the tropics. A similarly mixed avifauna has been found in the mid-Miocene beds of various other parts of France, Germany and Italy. In Colorado and New Mexico Marsh has detected bones ofMeleagris, Puffinus, SulaandUria, all existing genera; but the first is especially suggestive, since it is one of the most characteristic forms of the New World.
Here may be interpolated a short account of the very peculiar avifauna found in the Tertiary strata of Santa Cruz in Patagonia. Instead of the age of lower Eocene, as had been stated originally, these beds are not older than mid-Miocene, and not a few of the bones are of a much younger, even latest Tertiary date. Discovered, and partly described, by F. Ameghino, the bones have been sumptuously monographed by F.P. Moreno and A. Mercerat, who proposed for them the name ofStereornithes, a new order of birds, mostly gigantic in size, and said to combine the characters of Anseres, Herodiones and Accipitres. But the whole mass of bones is in hopeless disorder, apparently without any record of association. At any rate, the “Stereornithes,” accepted as such in Bronn’sThierreich, and in Newton’sDictionary of Birds, had to be dissolved as an unnatural, haphazard assembly. Many of these birds, to judge from the enormous size of their hind-limbs, were undoubtedly flightless,e.g.Brontornis, and remind us of the EoceneGastornisof Europe.Phororhacos, the most extraordinary of all, belongs to the Gruiformes, perhaps alsoPelecyornisandLiornis. On the other hand, the late TertiaryDryornisis a member of the Cathartae or American vultures, andMesembriornis, likewise of late Tertiary date, is a close forerunner of the recent genusRhea.
Pliocene remains are less numerous than those of the Miocene. From Pikermi in Greece is known aGallus, aPhasianusand a largeGrus. From Samos a large stork,Amphipelargus, and a typicalStruthio; from the Sivalik Hills on the southern flanks of the Himalayas also an ostrich, and another Ratite with three toes,Hypselornis, as well asLeptoptilus, PelecanusandPhalacrocorax. The fossil egg of a struthious bird,Struthiolithus, has been found near Cherson, south Russia, and in north China. The Suffolk Crag has yielded the unmistakable bones of an albatross,Diomedea.
Most Pleistocene birds are generically, even specifically, identical with recent forms; some, however, have become extinct, or they have become exterminated by man. A great number of birds’ bones have been found in caves, and among them some bearing marks of human workmanship. In France we have a large and extinct crane,Grus primigenia, but more interesting are the numerous relics of two species, the concomitants even now of the reindeer, which were abundant in that country at the period when this beast flourished there, and have followed it in its northward retreat. These are the snowy owl,Nyctea scandiaca, and the willow-grouse,Lagopus albus. A gigantic swan,Cygnus falconeri, is known from the Zebug cavern in Malta. From caves of Minas Geraes in Brazil, O. Winge has determined at least 126 species, of which nearly all still survive in the country. Kitchen-middens of England, Ireland and Denmark reveal the existence of the capercally,Tetrao urogallus, and of the great auk or gare-fowl,Alca impennis; both species long since vanished from those countries. In the fens of East Anglia have been found two humeri, one of them immature, of a truePelecanus, a bird now no longer inhabiting middle Europe.
Until a very recent epoch there flourished in Madagascar huge birds referable to the Ratitae,e.g.Aepyornis maximus, which laid enormous eggs, and not unnaturally recalls the mythical “roc” that figures so largely in Arabian tales. New Zealand has also yielded many flightless birds, notably the numerous species and genera ofDinornithidae, some of which survived into the 19th century (seeMoa);Pseudapteryxallied to theKiwi;Cnemiornis, a big, flightless goose;AptornisandNotornis, flightless rails; andHarpagornis, a truly gigantic bird of prey with tremendous wings and talons.
It is, of course, quite impossible, in a survey of extinct birds, to divide them into those which arebona fidefossil, sub-fossil, recently extirpated and partially exterminated. Nor is it possible, except in a few cases, to decide whether they have come to an end through the agency of man or through so-called natural causes. Like other creatures birds have come, some to flourish and stay, others to die out.
Mauritius is famous for the dodo, killed off by man; there was also a curiously crested parrot,Lophopsittacus(fig. 19). In the Mare aux Songes have been found the bones of another parrot, of ducks, pigeons, rails, herons, geese and of a dwarf darter,Plotus nanus, all sub-fossil, now extinct. Very interesting isAphanapteryx(fig. 20), a long-billed, flightless rail, practically the same asErythromachusof Rodriguez andDiaphorapteryxof Chatham Island. Réunion possessed the peculiar starling,Fregilupus. Rodriguez was inhabited byPezophaps, the solitaire,NecropsittacusandPalaeornis exsul, which is nowprobably extinct. The Antilles tell a similar tale. The great auk, once common on the British coasts, those of Denmark, the east coast of North America, then restricted to those of Newfoundland, Greenland and Iceland, has been killed by man, and the same fate has overtaken the Labrador duck, the Phillip Island parrot,Nestor productus, and the large cormorant of Bering Island,Phalacrocorax perspicillatus; and how long will the flightless cormorant,Ph. harrisiof the Galapagos, survive its quite recent discovery?