-34 ZOOLOGY sect. 



2. DISTI^fCTIVE Characters and Classification. 



The Eeptilia are cold-blooded Sauropsida (p. 313), with a horny 

 epidermal skeleton of scales, and frequently with an armour 

 of dermal bony plates. The centra of the vertebrae have 

 spheroidal articular surfaces. There are usually only two vertebrje 

 in the sacral region. The episternum, when present, always 

 remains distinct from the clavicles. The floor of the acetabulum 

 is often completely ossified. The pubes and the ischia usually 

 meet in ventral symphyses. The metatarsals do not become 

 ankylosed. The mandible, as well as several bones of the upper 

 jaw, very usually bear teeth. The optic lobes are situated on the 

 dorsal aspect of the brain. The ventricle is rarely divided by a 

 complete partition. There is always a paired aortic arch in the 

 adult. 



Order I. — Squamata. 



Reptilia in which the surface is covered with horny scales, 

 sometimes with the addition of dermal ossifications. The 

 opening of the cloaca is transverse in direction. There is a pair 

 of eversible copulatory sacs in the male. The vertebrae are nearly 

 always procoelous. The sacrum, absent in the Ophidia and some 

 Pythonomorpha, consists of two vertebrte in the Lacertilia. The 

 ribs have simple vertebral extremities. The quadrate is usually 

 movably articulated with the skull. There is no inferior temporal 

 arch. The nasal apertures of the skull are separate. The limbs, 

 when present, are sometimes adapted for terrestrial locomotion 

 (Lacertilia), sometimes for swimming (Pythonomorpha). The teeth 

 are acrodont or pleurodont (see helow). The lungs are simple sacs. 

 There is always a wide aperture of communication between the 

 right and left divisions of the ventricular cavity. The optic lobes 

 are approximated, and the cerebellum is extremely small. 



Sub- Order a. — Lacertilia. 



Squamata in which, as a rule, the limbs are present and are 

 adapted for walking. The mouth is capable of being opened to 

 only a moderate extent. The maxillae, palatines, and pterygoids 

 are incapable of free movement. The rami of the mandible are 

 firmly united at the symphysis. There are nearly always movable 

 eyelids and a tympanum. A sternum and an episternum are 

 present. 



Including all the Lizards, such as the Skincs, Geckos, Monitors, 

 Iguanas, Amphisbtenians, Chamaeleons, and other groups. 



Sub-Order b. — Ophidia. 

 Squamata with long narrow body, devoid of limbs. The mouth 

 is capable of being opened to form a relatively very wide gape by 

 divarication of the jaws. The maxillee, palatines, and ptery- 



