ORGANS OF CROCODILIANS. 



5«S 



ward 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 very 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, 

 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 seveial 

 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 

 behind 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 

 drowned, the Crocodilian keeps the tip of its snout above water, the 

 glottis is pushed forward to meet the posterior nares, a complete channel 

 for the passage of air is thus established, and respiration can go on un- 

 impeded. For their shore work the Crocodilians prefer the darkness, 

 but they often float basking in the , sun, with only the tip of the snout 

 and the ridge of the back exposed. ' 



Glands with a secretion which smells like musk are usually developed 

 on the margin of the lower jaw, at the side of the cloacal aperture, 

 and on the posterior margins of the dorsal scutes. The musky odour 

 is very strong during the pairing season, and when the animals are 

 attacked. . , . f . 



In connection with the muscular system, the presence of what is often 

 called an incipient diaphragm between the thoracic and the abdominal 

 cavity is of interest. . ... 



The brain seems very small in relation to the size of the skull. 



The eyes are provided with a third eyelid, as in most Reptiles, Birds, 



Fig. 255.— Half of the pelvic girdle 

 of a young crocodile. 



//., Ilium; a./., acetabulum; Is., 

 ischium ; P., pubis or epipubis. 



