140 REPTILIA CLASS in 



Class 3. REPTILIA.' 



Cold-blooded, naked, scaly or armoured vertebrates, with exclusively pulmonary 

 respircttion, and terrestrial or aquatic in habit. Skeleton completely ossified ; embryo 

 with amnion and allantois, development without metamorphosis. Skull with a single 

 basioccipital condyle. Two pairs of limbs usually present ; metapodal bones separate. 



In external appearance reptiles closely resemble amphibians, but are 

 vastly more difterentiated as a class, and are mostly of greater size. Their 

 extremities exhibit great diversity in structure and function. Among the 

 Pterosauria the anterior limb is transformed into a volant organ provided 

 with a flexible wing membrane ; among Dinosaurs the appendicular skeleton 

 attains a size and ponderosity unsurpassed by the largest land mammals ; in 

 marine reptiles the limbs are paddle-shaped ; and in most Lacertilians, Thero- 

 morphs, Crocodiles, and Dinosaurs the limbs are ambulatory ; while the only 

 apodal forms occur among the Squamata (snakes and certain lizards). 



The integument of reptiles is tougher than that of amphibians, and a more 

 or less perfect exoskeleton is often developed in consequence of the ossifica- 

 tion of the cutis and cornification of the epidermis. The former may give 

 rise to bony scutes overlapping one another in a tectiform manner, or to 

 larger bony plates with closely applied edges, arranged so as to form a more 

 or less continuous shield, as in tortoises. 



The vertebral column is always ossified, although remnants of the notochord 

 may persist in the centra. In all cases where both pairs of limbs are present, 

 cervical, dorsal, sacral, and caudal regions are distinguishable, and the dorsal 

 series may be often subdivided into thoracic and lumbar vertebrae. The 

 vertebral centra exhibit all gradations between amphiplatyan, amphicoelous, 

 procoelous, and opisthocoelous ; and the union between the centra and their 

 neural arches may be cartilaginous, sutural, or by anchylosis. The neural 

 spines are always ossified. Sometimes they are enormously produced, in 

 other cases (Chelonia.) laterally expanded and united with dermal plates. The 

 anterior zygapophyses have facettes looking inward and upward which are 

 overriden by the post-zygapophyses of the vertebra immediately in front ; and 

 in the Squamata and Dinosaurla the vertebrae are still further conjoined by a 

 median process given off from the anterior {zygosphene) or posterior {hyposphene) 

 end of the neural arch, and received into a notch of the arch next behind 

 (zygantrum) or in front (hypantrum). The cervicals generally bear short 

 tranverse processes (diapophyses) attached to the sides of the centra, but in 

 the dorsal series these processes are given off from the neural arches. The 

 haemapophA^ses or " chevron bones " of the caudal series sometimes form true 



^ Literature : 



Baur, G., On the phylogeuetic arrangenieut of the Sauropsida (Journ. Mori^hol. vol. I. No. 1), 

 1887. — Bernerkungen iiber die Osteologie der Schlafengegend der liciheren Wirbelthiere (Anat. 

 Anz. vol. X. p. 315), 1894 — Co2ye, E. D., Synopsis of the extinct Batrachia, Reptilia and Aves 

 of North America (Traus. Anier. Phil. Soc. vol. XEV.), 1869. — Ou the homologies of the posterior 

 cranial arches in the Reptilia {ibid. vol. XVII.), 1892. — Furbringer, M., Zur vergleichenden 

 Anatomie des Brust^chulterapparats und der Schultermuskeln. IV. Theil. (Zeitschr. fiir Naturwis- 

 seusch. vol. XXXIV.), 1900. — Hoffnuom, C. K., Die Reptilien, in Broun's Classen nnd Ordnungeu 

 des Thierreichs, vol. VI. })t. 3, 1879-89. — Lydekker, R., Catalogue of the fossil Reptilia and 

 Amphibia in the British Museum, vols. I. -IV. London, 1888-90. — Meyer, II. von, Zur Fauna, der 

 Vorwelt. Ft. I.-IV. Frankfort. 1845-60.— Oife?i, R., Report on British fossil Reptilia (Rept. 

 Brit. Assoc. Adv. Sci. 9th Meet.' p. 43), 1839. Also ibid, llth Meet. p. 60, 1841.— A History of 

 British fossil Reptiles [Reprint]. Loudon, 1849-84. 



