336 ZOOLOGY sect. 



In essentials the heart and brain resemble those of the Squamata. 

 There are no copulatory sacs, but a median penis. 



This order includes the Land Tortoises, Soft Tortoises, River 

 and Mud Tortoises, and the Turtles, besides a number of fossil 

 forms. 



Order IV. — Theromorpha. 



Extinct Reptiles with amphiccBlous vertebrae sometimes enclosing 

 remnants of the notochord, with a sacrum composed of from two 

 to six vertebrae, and with ribs having bifid vertebral extremities. 

 The quadrate is not movable. The limbs are adapted for walking. 

 The pubes and ischia are united. The teeth, which are usually, 

 though not always, present, are highly differentiated and lodged 

 in sockets, 



This order comprises a large number of extinct Reptiles, which 

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

 Pareiosauria, and Theriodontia (Fig. 1011). 



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 proccelous. The anterior thoracic vertebrae 

 have elongated and bifid transverse processes. The sacrum 

 consists of two vertebras. 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 com- 

 pound 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. 



Tliis 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 fiipper-like limbs. The centra are slightly 

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

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

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

 teeth are situated in sockets (Fig. 1012). 



Order VII. — Ichthyopteeygia. 



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 premaxillae are drawn out • to form an .elongated rostrum. 



