326 ZOOLOGY SECT. 



This order comprises a large number of extinct Reptiles, which 

 are grouped in the four sub-orders Anomodontia, Placodontia, 

 Pareiosauria, and Theriodontia (Fig. 1022). 



ORDER V. CROCODILIA. 



Reptiles in which the dorsal surface, or both dorsal and ventral 

 surfaces, are covered with rows of sculptured bony scutes supporting 

 horny scales. The vertebral centra are either amphiccelous, flat 

 at each end, or procoelous. The anterior thoracic vertebrae have 

 elongated and bifid transverse processes. The sacrum consists 

 of two vertebrae. The ribs are bifid at their vertebral ends. The 

 quadrate is immovable. A sternum is present, and there is a 

 series of abdominal ribs. The limbs are adapted for walking. 

 The teeth are lodged in sockets. The lungs are compound sacs. 

 The ventricle of the heart is completely divided in recent forms. 

 The opening of the cloaca is elongated in the direction of the long 

 axis of the body. There is a median penis. 



This order includes among living forms the true Crocodiles, the 

 Gavials, the Alligators, and Caimans. 



ORDER VI. SAUROPTERYGIA. 



Extinct aquatic Reptiles with elongated neck, small head, short 

 tail, and usually flipper-like limbs. The centra are slightly 

 amphiccelous or quite flat. The sacrum is composed of either one 

 or two vertebrae. The cervical ribs are bifid, the thoracic simple. 

 The quadrate bone is immovable. There is no sternum. The 

 teeth are situated in sockets (Fig. 1023). 



ORDER VII. ICHTHYOPTERYGIA. 



Extinct aquatic Reptiles, with large head, without neck, 

 and with elongated tail and completely flipper-like limbs. The 

 centra are amphiccelous, and there is no sacrum. The ribs are 

 bifid at their vertebral ends. The quadrate is immovable. The 

 premaxillse are drawn out to form an elongated rostrum. There 

 is no sternum, but there is a series of abdominal ribs. The 

 teeth are lodged in a common groove. The integument is naked 

 (Fig. 1026). 



ORDER VIII. DINOSAURIA. 



Extinct terrestrial Reptiles with elongated limbs, having the 

 surface sometimes naked, sometimes provided with a bony armour. 

 The centra are usually amphiccelous. The sacrum consists of 

 from two to six vertebrae. The ribs are bifid. A sternum is 

 present. The quadrate is fixed. The pelvis usually resembles 

 that of a Bird, the ilium being extended fore and aft, and the 

 pubis, as well as the ischium, directed backwards. The teeth 



