226 TROPICAL MEDICINE AND HYGIENE 



the pterygoid to the maxilla, and in many poisonous 

 snakes acts as a lever for the erection of the latter. This 

 function of the transpalatine is very evident in all the 

 vipers ; when the mouth is opened the distal end of the 

 quadrate is advanced, the pterygoid and transpalatine 

 are thus thrust forward, and the maxilla consequently 

 is erected. This movement of the maxilla is quite limited 

 in the Colubridce. 



The teeth of snakes are merely recurved hooks for 

 holding the prey, which is bolted whole. Teeth may 

 be present on all the bones that compose the jaws and 

 palate, except the transpalatine. Their attachment 

 (ankylosis) to the bone is superficial, and they are easily 

 broken off, but are readily renewed. In- some snakes 

 some of the larger teeth are longitudinally grooved on 

 their anterior, convex surface, to carry saliva into the 

 bite, and in the venomous snakes these enlarged and 

 channelled teeth form the poison-fangs, which are 

 described further on. 



Animals that may be confused with Snakes There are 

 numerous snake-like lizards ; and also the burrowing, 

 limbless amphibia of the order Apoda may be mistaken 

 for snakes. Again, in Indo-Pacific waters, eels and sea- 

 snakes might be confounded. Even earthworms have 

 sometimes caused perplexity to undiscriminating 

 observers. Quite apart from morphological differences 

 that are discovered by dissection, snakes can always 

 be distinguished by the absence of a bony mandibular 

 symphysis, and by their long, forked, protrusible tongue, 

 retractile into a basal sheath. There are lizards and 

 some of them are snake-like that have a forked, and 

 even a more or less protractile, tongue ; but the only 

 lizards whose tongue is quite snake-like possess well- 

 developed limbs. Some of the limbless lizards, again, 

 have movable eyelids and an external ear-opening. In 

 the snake-like apodous Amphibia the cloacal orifice is 

 at the very end of the body ; there is usually, behind 

 each nostril, a small pit containing a papilla-like tentacle ; 



