2Q2 CLASSIFICATION OF VERTEBRATES. 



characteristic of the sauropsida. The skin is remarkably defi- 

 cient in glands, these, when present, usually occurring upon the 

 legs or upon the tail. The characteristic scales are cornifica- 

 tions of the epidermis, and are occasionally re-enforced by bony 

 plates developed in the dermis. The single occipital condyle is 

 situated on the basioccipital, the exoccipitals contributing to its 



pa;o 



FIG. 291. Base of skull of alligator, showing the single occipital condyle. bo, 

 basioccipital; bs, basisphenoid ; eo, exoccipital; et, opening of Eustachian tube;/w, 

 foramen magnum ; pao, paroccipital ; //, pterygoid ; q, quadrate ; qj, quadratojugal ; 

 sg, squamosal ; tr, transversum. 



formation to a varying extent. The mandible consists of a single 

 cartilage bone, the articulare, and at most five membrane bones, 

 dentary, splenial, coronoid, angulare, and surangulare. The 

 cervical ribs are usually well developed, the neck passing insen- 

 sibly into the thorax. The ovarian ducts have their inner ends 

 entire as in the ichthyopsida. 



The sauropsida contains the Reptilia and the Aves. 



SUB-CLASS I. REPTILIA. 



Cold-blooded amniotes ; the external surface of the body 

 (except in a few fossil forms) covered with horny epidermal 

 scales or bony dermal plates ; anterior appendages, when present, 

 ambulatory (except in pterodactyls), the carpals and meta- 

 carpals numerous ; sacral vertebrae usually two ; pubic and is- 

 chiadic bones united by symphysis, except in some dinosaurs ; 

 persisting right and left aortic arches. 



