712 



PHYLUM CHORDATA : CLASS REPTILIA 



In the pelvic arch, large ilia are united to the strong ribs of the two 

 sacral vertebrae ; the pubes, or more strictly the epipubes, slope 

 forward and inward, and have a cartilaginous symphysis ; the ischia 

 slope backward and have a symphysis ; ilia and ischia form almost 

 the whole of the acetabulum, a small part being occupied by the true 

 pubes. The hind-limbs bear four digits, webbed and clawed. 



Organs of Crocodilians. — The Crocodilians are seen to best 

 advantage in the water, swimming by powerful tail-strokes. The limbs 

 are too weak for ver^^ effective locomotion on land, the body drags 

 on the ground, and the animals are stiff-necked. Although many, 

 especially in their youth, feed on fishes and small animals, the larger 

 forms lurk by the edge of the water, lying in wait for mammals of 

 considerable size. These they grasp in their extremely powerful jaws, 



aK.3.. 



Fig. 421. — First five cervical vertebrae of crocodile. — From a 



Specimen. 



I, Pro-atlas ; 2, lateral portion of atlas ; 3, ventral portion of atlas ; 



4, first cervical rib. 

 n.sp., Neural spine of axis ; o.p., odontoid process of axis ; C.R.2, 



second cervical rib ; C.R.3, third cervical rib. 



and drown by holding them under water. If the dead booty cannot 

 be readily torn, it is often buried and left until it begins to rot. In 

 connection with their way of feeding, we should notice several 

 peculiarities of structure : the nostrils are at the upper end of the 

 snout, and the eyes and ears are also near the upper surface, so that 

 the Crocodilians can breathe, see, and hear while the body is alto- 

 gether immersed except the upper surface of the head ; the nostrils can 

 be closed by valves, and the eyes by transparent third eyelids, and 

 the ears by movable flaps, so that the head can be comfortably im- 

 mersed ; a flat tongue is fixed to the floor of the mouth, and the 

 cavity of the mouth is bounded beliind by two soft transverse mem- 

 branes, which, meeting when the reptile is drowning its prey, pre- 

 vent water rushing down the gullet ; the posterior opening of the nostrils 

 is situated at the very back of the mouth, and when the booty is being 



