74 INTRODUCTION 



organ, richly provided with nerves, communicates 

 with the inside of the mouth, its function may be to 

 smell the prey as it passes through previous to de- 

 glutition. Snakes cannot be credited with a keen 

 sense of smell, although undoubtedly guided by it 

 during the nuptial period. 



In the more thoroughly aquatic snakes, the nostril 

 may be closed, when respiration is suspended, by a 

 spongy tissue, which acts as a stopper, and such nos- 

 trils are called "valvular," although a valve is not, in 

 the strict sense, present ; when the animal breathes, 

 the nostril is opened by a compression, through special 

 muscles, of the cavernous tissue. In some Sand- 

 snakes the narial opening may be reduced to a 

 crescentic slit. 



The sense of hearing is not much developed. 

 Tympanum, tympanic cavity, and Eustachian tubes 

 are absent. In the typical snakes a long columellar 

 rod (the stapes), with a fibrous or cartilaginous pad at 

 the outer end, extends from the fenestra ovalis in the 

 cranium to the quadrate, but in the degraded burrow- 

 ing forms the stapes is a small bony plate closing the 

 fenestra ovalis. 



With one exception (Eryx jaculus, which is said by 

 Schreiber to lap like a lizard), the tongue is not used 

 for drinking or for the prehension or gustation of 

 food, nor for hissing, but is a tactile organ protruded 

 on any object the snake wishes to probe. It is slender 

 and deeply bifid at the end, smooth, very protractile, 



