YOUNG CROCODILIANS IN CAPTIVITY. 167 



rest downward on the top and sides of the back and tail, 

 when they can rub off anything that clings to them. 



The head presents some interesting points. The first is 

 that the nostrils can be closed by a valve action when 

 under water. There is a third and transparent eye-lid 

 for use in the same element, and the opening of the ear 

 can be closed at will. 



The cavity of the mouth is very shallow, and they 

 have tremendous crushing powers in their jaws. The 

 palate is grooved for the reception of the tongue, which is 

 always fixed, and in every species is either white or pale 

 yellow. The epiglottis is prolonged upwards and for- 

 wards, lying in contact with the palate, thus shutting off 

 the mouth cavity from the gullet and windpipe. The 

 posterior nares open behind this screen enabling the 

 creature to retain prey in its mouth under water without 

 danger of suffocation. All crocodilians are oviparous, 

 the eggs being rough and white, and about the size of a 

 ffoose egg. 



Four of the six genera are fairly frequently met with 

 the true crocodiles, the broad-fronted West African 

 crocodile, the alligators, and the caimans. The remaining 

 genera are, the gavials and a connecting form known as 

 Tomistoma, coming from Borneo, and related to both the 

 Gavials and the crocodiles. These are seldom imported. 

 The former is said to be almost exclusively fish eating. 



Crocodiles usually have the fourth mandibular tooth 

 fitting into a notch in the upper jaw; the teeth of both 

 jaws interlock, and the nasal bones, while entering the 

 nasal aperture, do not form a bony septum. Then the 

 teeth in the lower jaw do not number more than fifteen on 

 each side. Needless to say, the quadrate bone is 

 immovably united to the skull. The broad-fronted 

 crocodile is the only species of its genus, Osteolcemus, and 



