5 8 4 



REPTILES. 



The tail is laterally compressed and assists in swimming. 



Teeth occur in distinct sockets 

 in the premaxillcz, maxilla, 

 and dentaries. 



In modern Crocodilians, al- 

 most all the vertebra are pro- 

 ccslous. 



The skull has many char- 

 acteristic features, such as the 

 union of maxillce, palatines, 

 and pterygoids in the middle 

 line on the roof of the mouth, 

 and the consequent shunting of 

 the posterior nares to the very 

 back of the mouth. 



Some of the ribs have double 

 articulating heads, and bear 

 small uncinate processes some- 

 what like those of birds ; trans- 

 verse ossifications associated 

 with the subcutaneous fibrous 

 tissue of the abdomen from so- 

 called abdominal ribs. 



The heart is four chambered; 

 a muscular diaphragm par- 

 tially separates the thoracic 

 from the abdominal cavity. 



The cloaca has a longitudinal opening. 

 a grooved penis. 



The Crocodilians are oviparous. The eggs have firm cal- 

 careous shells, and are laid in holes in the ground. 



Some of the Characteristic Features in the Skeletal System of 

 Crocodilians. 



(These notes on the skeleton are in great part taken from Huxley's 

 Manual.) 



Numerous transverse rows of sculptured bony plates or scutes, ossified 

 in the dermis, form a dorsal shield. On the ventral surface the scutes 

 are absent, except in some alligators, in which they are partially ossified. 

 But besides and above the scutes, there are horny epidermic scales like 

 those in other Reptiles. The hide is often used as leather. 



The vertebral column consists of distinct cervical, dorsal, lumbar, 



FIG. 201. Lower surface of 

 skull of a young Crocodile. 



P.mx., Premaxilla ; mx., maxilla ; 

 pal., palatine; o.t., os transversum ; 

 pt., pterygoid ; /., jugal ; Q.j., quad- 

 rato-jugal ; Q., quadrate; p.n., pos- 

 terior nares ; c., condyle. 



The males have 



