then spreads nearly all over the inner side of the egg-shell. Having thus come into the closest possible contact with the atmospheric air, the vessels of the allantois can exchange their carbon dioxide for oxygen and the allantois becomes the respiratory organ of the embryo. Herewith stands in direct correlation the complete absence of any internal and of external gills in the embryonic reptiles. The blood vessels of the allantois are fundamentally the same as those of the batrachian bladder, namely, branches from the pelvic arteries (later hypogastrics) and veins which return from the base of the bladder to the abdominal wall and thence to the liver.
In the normal reptilian egg, surrounded by its non-yielding shell, space is absolutely limited, and whilst the yolk is being diminished and increased secretion of urine distends the bladder, this soon protrudes out of the body cavity proper into the extra-embryonal coelomatic space between the true amnion and the false amnion or serous membrane. It fills this space so far as the yolk-sac allows it. It seems reasonable to suppose that this growth of the allantois has been one of the causes of the caudal amniotic fold; the sinking of the embryo into the space of the diminishing yolk-sac is no doubt another cause, but the fact remains that the amnion is the chief hindrance to the closing of the body-wall at the region of the future navel.
The life-histories of embryonic development are the domain of the embryographers. They are the imperfect accounts of the ways and means (often crooked and blurred, owing to short cuts and in adaptation to conditions which prevail during the embryonic period) by which the growing creature arrives at those features which form the account of the anatomical structure of the adult. Comparative anatomy, with physiology, alone lead through the maze of the endless embryonic vagaries and afford the clues for the reconstruction of the real life-history of an animal and its ancestry. For detail the reader is referred to numerous papers quoted in the list of literature, and to the various text-books, above all to the Handbuch d. vergleichenden Entwicklungsgeschichte d. Wirbelthiere, edited by O. Hertwig, Berlin.
Authorities on Anatomy: Bibliography.—The appended list of papers (many with shortened titles) represents but a fraction of the enormous literature dealing with the anatomy of reptiles. Special stress has been laid upon the more recent publications. A great amount of information, general and detailed, is contained in Bronn's Klassen u. Ordnungen d. Thierreichs, the three volumes concerning reptiles having been written by C. K. Hoffmann (Leipzig, 1878-1890); E. D. Cope's Crocodilians, Lizards and Snakes of North America, U.S. Nat. Mus., Washington, 1900; H. Gadow's “Amphibia and Reptiles,” vol. xiii. of The Cambridge Natural History (London, 1901); above all in C. Gegenbaur's Vergleichende Anatomie d. Wirbelthiere (Leipzig, 1898-1901).
Skeletal.—J. F. v. Bemmelen, “Schaedelbau v. Dermochelys coriacea,” Festschr. f. Gegenbaur (1896); E. Gaupp, “Morphologie d. Schaedels,” Morpholog. Arbeiten (1894), iv. pp. 77-128, pls.; ibid. (“Problems Concerning the Skull”), Anat. Ergebn. (1901), x. pp. 847-1001. W. K. Parker, “Skull of Lacertilia,” Phil. Trans. 170 (1880), pp. 595-640, pls. 37-45; “of Tropidonotus,” ibid. (1879), 169, pp. 385-417, pls.; “Crocodilia,” Trans. Zool. Soc. (1885), xi. pp. 263-310, pls.; “Chamaeleons,” ibid. (1885), xi. pp. 77-105, pls. 15-19.; F. Siebenrock, “Kopfskelet d. Scincoiden, Anguiden u. Gerrhosauridan,” Ann. Nat. Hofmuseum (Wien, 1892), vii. 3. Of the enormous, still increasing, literature concerning the homologies of the auditory ossicles, a few only can be mentioned; the papers by Kingsley and Versluys contain most of the previous literature: W. Peters, several most important papers in Monatsber. Ak. Wiss. (Berlin, 21st Nov. 1867, 5th Dec. 1867, 7th Jan. 1869, 17th Jan. 1870, 15th Jan. 1874). H. Gadow, “Modifications of the First and Second Visceral Arches, and Homologies of the Auditory Ossicles,” Phil. Trans. 179 (1888), B. pp. 451-485, pls. 71-74; “Evolution of the Auditory Ossicles,” Anat. Anz. (1901), xix. No. 16. J. Versluys, “Mittlere u. äussere Ohrsphäre d. Lacertilia u. Rhynchocephalia,” Zool. Jahrb. Anat. (1898), 12, pp. 161-406, pls. (most exhaustive and careful); ibid., “Entwickl. d. Columella auris b. Lacertiliern,” ibid. (1903), 18, pp. 107-188, pls.; J. S. Kingsley, “The Ossicula auditus,” Tufts College Studies, No. 6 (1900). E. Gaupp, “Columella auris,” Anat. Anz. (1891), vi. p. 107. T. H. Huxley, “The Representatives of the Malleus and Incus of the Mammalia in the other Vertebrata,” P.Z.S., 1869. W. K. Parker, “Struct. and Development of Crocodilian Skull,” Trans. Zool. Soc. (1883), xi., especially pls. 68 and 69. H. Gadow, “Evolution of the Vertebral Column of Amphibia and Amniota,” Phil. Trans. (1896), 136, pp. 1-57 (with a list of ninety-three papers). G. B. Howes and H. H. Swinnerton, “Development of the Skeleton of Sphenodon,” Trans. Zool. Soc. (1901), xvi. pp. 1-86, pls. 1-6. G. A. Boulenger, Catalogue of Chelonians, Rynchocephalians and Crocodiles, Brit. Mus. 1889; Cat. of Lizards (3 vols., 1885-1887); Cat. of Snakes (3 vols., 1893-1896); these volumes contain a great body of osteological observations, ignored by most compilers of anatomical text-books; “Osteol. of Heloderma, and Vertebrae of Lacertilia,” P.Z.S., pp. 109-118 (1891). L. Calori, “Skeleton of Varanus, Lacerta,” Mem. Acc. Sci. Instit. Bologna (8, 1857, and 9, 1859). E. D. Cope, “Osteology of Lacertilia,” Proc. Am. Phil. Soc. (1892), 30, pp. 185-221; “Degeneration of Limbs and Girdles,” Journ. Morph. (1892), vii. pp. 223-244. E. Ficalbi, Osteologia del Platidattilo (Pisa, 1882). A. Goette, “Beiträge z. Skeletsystem,” Arch. micr. Anat. (1877), 14, p. 502-620. A. Günther, “Anatomy of Hatteria,” Phil. Trans. (1867), 157, pp. 595-629, pls. S. Orlandi, “Note anatomiche s. Macrosincus,” Atti S. Lig. (Geneva, 1894), v. 2; “Skelet d. Scinc. Anguid. Gerrhosaurid,” Ann. Naturhist. Hofmus. (1895), x. pp. 17-41; “Skelet d. Agamidae,” Sitzb. Ak. Wiss. Wien (1895), 104, pp. 1089-1196. F. Siebenrock, “Skelet v. Brookesia,” Sitzb. Ak. Wiss. Wien (1893), 102, pp. 71-118; “Skelet v. Uroplates,” Annal. Naturhist. Hofmuseum (1892), vii. pp. 517-536, 1893; “Skelet d. Lacertiden,” Sitzb. Ak. Wiss. Wien (1894), 102, pp. 203-292. C. Smalian, “Anat. d. Amphisbaenid,” Zeitschr. wiss. Zool. (1885), 42, pp. 126-202. A. Voeltzkow, “Biolog. u. Entwickl. von Crocodilus,” Abh. Senckenb. Ges. (1899), 26, pp. 1-150, 17 pls. E. A. Case, “Osteology and Relationships of Protostega,” Journ. Morph. (1897), xiv. pp. 21-60. H. Goette, “Entwickl. des Carapax d. Schildkroeten,” Zeitschr. wiss. Zool. (1899), 66, pp. 40-434, pls. O. P. Hay, “ Morphogeny of Chelonian Carapace,” Amer. Nat. (1898), 32, pp. 929-948. G. Baur, “Morphol. Unterkiefer d. Rept.,” Anat. Anz. (1896), xi. pp. 410-415. M. Fürbringer, “Brustschulterapparat und Schultermuskeln. Reptilien,” Jena Zeitschr. (1900), 34, pp. 215-718, pls. 13-17 (with a list of many titles of papers concerning reptiles; and a new, unsatisfactory classification of the whole class). C. K. Hoffmann, “Becken d. Amphib. u. Reptil.,” Niederl. Arch. f. Zool., iii. E. Mehnert, “Beckenguertel d. Emys lutaria,” Morph. Jahrb. (1890), 16, pp. 537-571, pl.; “Os hypoischium, &c. d. Eidechsen,” Morph. Jahrb. (1891), 17, pp. 123-144, pl. W. K. Parker, “Shoulder Girdle and Sternum,” Roy. Soc. London, 1868. A. Rosenberg, “Development of Skeleton of Reduced Limbs,” Zeitschr. wiss. Zool. (1873), 23, pp. 116-170, pls. A. Sabatier, “Comparaison des ceintures et des membres ant. et post,” Mém. Ac. Montpellier (1880), xix. C. Gegenbaur, Untersuch. z. verg. Anat., “I. Carpus u. Tarsus” (1864), II. “Schulterguertel” (1865) (the most important monographs). A. Banchi, “Parafibula,” Monitore Zool. Italiano (1900), xi. No. 7 (A nodule ][ between femur and fibula in Lacerta). G. Baur, “Carpus u. Tarsus d. Reptil.,” Anatom. Anzeig. iv. No. 2. G. Born, “Carpus u. Tarsus d. Saurier,” Morph. Jahrb. (1876), 2, pp. 1-26, pl. A. Carlsson, “Gliedmassenreste bei Schlangen,” Svensk. Vetensk. Ac. Handlingar, ii. (1886). A. Johnson, “Development of Pelvic Girdle,” Q.J.M.S. (1883), 23, pp. 399-411. G. Kehrer, “Carpus u. Tarsus,” Ber. Naturf. Ges. (Freiburg, i. 1886). W. Kuekenthal, “Entwickl. d. Handskelets des Crocodiles,” Morph. Jahrb. (1892), 19, pp. 42-55. H. F. Sauvage, “Membre antérieur du Pseudopus,” Ann. Sci. Nat.-Zool. 7. art. 15 (1878). A. Stecker, “Carpus u. Tarsus bei Chamaeleon,” Sitzb. Ak. Wiss. (1877), 75, 2, pls. R. Wiedersheim, Gliedmassenskelett, Schulter u. Beckenguertel (Jena, 1892). K. Baechtold, Über die Giftwerkzeuge der Schlangen (Tübingen, 1843). A. Dugès, “Venin de l'Heloderma,” Jubil. Soc. Biol. (1899), pp. 34-137. F. Weinland, “On the Egg-tooth of the Snakes,” Proc. Essex Institute (Salem, 1856); and in Württemb. Jahresheft. Verein vaterl. Naturk. (1856). G. S. West, “Buccal Glands and Teeth of Poisonous Snakes,” P.Z.S. (1895), pp. 812-826, pls. 44-46.
Tegumentary.—A. Batelli, “Bau der Reptilienhaut,” Arch. mikr. Anat. (1880), 17, pp. 346-361, pls. J. E. V. Boas, “Wirbelthierkralle,” Morph. Jahrb. (1894), xxi. p. 281-311, pls. A. Haase, “ Bau d. Haftlappen bei den Geckotiden,” Arch. Naturg. (1900), 61, pp. 321-345, ps. R. Keller, “Farbenwechsel d. Chamaeleons,” Arch. ges. Physiol. (1895), 61, pp. 123-168. C. Kerbert, “Haut der Reptilien,” Arch. mikr. Anat. (1876), 13, pp. 205-262. F. Maurer, Epidermis und ihre Abkoemmlinge (Leipzig, 1895). F. Schaefer, “Schenkeldruesen d. Eidechsen,” Arch. Naturg. (1902), 68, pp. 27-64, pls. F. Todaro, Ricerche f. nel labor. di anat. norm. di Roma (1878), II. 1. F. Toelg, “Drüsenartige Epidermoidalorgane d. Eidechsen u. Schlangen,” Arb. Zool. Inst. Wien (1904), 15, pp. 119-154, pls.
Nervous System.—J. F. Bemmelen, “Beitr. Kenntniss d. Halsgegend bei Reptilien Mededeel,” Natura Artis Magistra (Amsterdam, 1887). L. Edinger, “Zwischenhirn d. Reptilien,” Abh. Senckenb. Ges. (1899), 20, pp. 161-197, pls. J. G. Fischer, “Gehirnnerven d. Saurier,” Abhandl. Naturwiss. Verein, Hamburg, II. (1852), pp. 115-212 (with many excellent illustrations). M. Fürbringer, “Spinooccipital Nerven,” &c., Festschr. f. Gegenbaur, iii. (1896). S. P. Gage, “Brain of Trionyx,” Proc. Arn. Micr. Soc. (1895), xvii. pp. 185-222. E. Gaupp, “Anlage d. Hypophyse b. Sauriern,” Arch. mikr. Anat. (1893), 42, pp. 569-680. Giuliani, “Struttura d. midolla spinale d. Lacerta viridis,” Ric. Lab. di Anat. Roma, ii. J. Grimm, “Rückenmark v. Vipera berus,” Arch. Anal. Phys. (1864),
