108 COMPARATIVE DENTAL ANATOMY 



body of the snake itself. A toad, twice or three 

 times the diameter of a snake, can be swallowed 

 by working the jaws up over it gradually, ad- 

 vancing first one jaw and then the other, the re- 

 curved teeth holding the bite as it progresses and 

 thus forcing the object slowly downward into the 

 oesophagus. The teeth of the serpents are very 

 uniform, — of simple conical shape, recurved and 

 very sharp, — and are used for prehension only. 

 The cone-shape tooth attains its most perfect de- 

 velopment, is largest and longest in this order, 

 as illustrated in the poison fangs of serpents. 

 The number of teeth varies extensively, and they 

 are supported by the maxillaries, dentary, ptery- 

 goid bones and the mandible. The poisonous 

 species are armed with the poison fang, which is 

 long and sharp and grooved or is formed into a 

 tube to inject the poison hypodermically (Fig. 

 35). Some poison fangs are erectile, as the Eat- 

 tlesnake; others are upright and rigid, as the 

 Cobra. They are connected by the basal open- 

 ing of the tube with the poison sac, which occupies 

 the temporal muscles when the mouth is widely 

 distended. The tubular tooth through which the 

 poison flows and is injected into the flesh is 

 formed as if a conical tooth had been flattened 

 into a thin sheet and then rolled so that the edges 

 were brought together to form a tube, so that all 

 the tissues are flat, even the pulp, — the inside of 



