REPTILIA. 441 



noticed in the skate, have been more fully described in 

 the chick, p. 380.) 



Again, the reptiles have twelve cranial nerves, the spinal 

 accessory and hypoglossal being added to the ten of 

 Amphibia, and the skeleton is much more completely ossi- 

 fied than is the case in the latter. The body is usually 

 protected in an exoskeleton of scales or scutes, which is 

 either purely epidermic and cuticular in nature, or is dermal 

 and formed of bony tissue 



In the skeleton the reptiles have the typical pentadactyle limbs and 

 the ankle-joint is intertarsal. The shoulder-girdle usually has clavicles 

 and episternum as well as the three primary bones — the precoracoid, 

 coracoid and scapula. In the pelvic-girdle the ilium usually fuses with 

 two sacral vertebrae and there are usually epipubic bones. There are 

 often a number of membrane-bones called abdominal ribs. In the skull 

 the quadrate suspends the lower jaw which is composed of several 

 bones ; the teeth are polyphyodont and homodont and are attached to 

 the surface of the bone (acrodont) or at the side (pleurodont), and they 

 may occur on the palatines, pterygoids and vomers, as well as the 

 premaxillge, maxillae and dentary. The skull has a single occipital 

 condyle, formed largely by the basioccipital but partly by the ex- 

 occipitals, and the facial portion of the skull is much larger and broader 

 than the cranial. There is 'often a peculiar transverse bone connecting 

 the maxilla and the pterygoid. There is only one ear- ossicle, the 

 columella aiiris. 



Most of the reptiles resemble the amphibians in the 

 three chambered heart, the three complete aortic arches and 

 the condition of the circulatory system. 



Order I . — Rhynchocephalia. 



Sphenodon (or the New Zealand Lizard) is a lizard-like 

 animal, found in New Zealand, possessing a series of 

 primitive structural peculiarities which lead zoologists to 

 place it in an order by itself. The principal of these are the 

 amphicoelous vertebrae, the presence of intercentral elements 

 between the vertebrae and of teeth on the palatines and 

 vomers (young). 



Order II. — Lacertilia. 



The lizards have an exoskeleton of horny epidermic 

 scales which are periodically shed. Most have two pairs of 

 walking limbs and a long tail. The teeth are either fused 



