314 ZOOLOGY i< i 



vertebne have elongated and bifid transverse processes. The sacn 1 1 1 

 consists of two vertebra 1 . 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. 



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 

 amphicoelous or quite flat. The sacrum is composed of 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. 953). 



ORDER VII. ICHTHYOPTERYGIA. 



Extinct aquatic Reptiles, with large head, without neck, and 

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

 are amphicoelous, and there is no sacrum. The ribs are bifid 

 at their vertebral ends. The quadrate is immovable. The pre- 

 maxillae are drawn out to form an elongated rostrum. There is no 

 sternum, but there is a series of abdominal ribs. The teeth an 

 lodged in a common groove. The integument is naked (Fig. 956). 



ORDER VIII. DINOSAURIA. 



Extinct terrestrial Reptiles with elongated limbs, having the 

 surface of the body sometimes naked, sometimes covered with a 

 bony armour. The centra are amphiccelous or opisthocoelous. 

 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 are lodged in sockets, and have compressed crowns 

 (Fig. 957). 



ORDER IX. PTEROSAURIA. 



Extinct Reptiles, the structure of which is greatly modified in 

 adaptation to a flying mode of locomotion. The vertebra- are 

 procoelous, the neck elongated. The sacrum contains three or four 

 vertebrae. The anterior thoracic ribs are bifid. The skull resembles 





