THE OPHIDIA. 23 



however, are, in common with the rest, perfectly dry and clean. 

 The tongue of a snake acts as a feeler, an instrument of touch 

 and of investigation, particularly in the dark, conveying informa- 

 tion of surroundings — so to speak — to the owner of the delicate 

 organ. It is formed of a double muscle, or pair of muscles 

 united from the root to near the tip, where they divide, and 

 terminate in those slender, hair- like filaments which are so alarm- 

 ing to the ignorant. The illustrations (fig. 6) are from nature and 

 the exact size. The largest (a) is that of a Jamaica boa; the 

 small slender tongue (b) is that of a South-American snake some- 

 what smaller than our English ring-snake ; and the shortest (c) is 

 that of a very young African viper, a short and stout little reptile 



Fig. 6. — Illustration of tongues. From nature by the Author. 



that has imparted this character to its tongue. The tongue of the 

 British viper would be slender and larger than b. Being so 

 delicately constructed and liable to injury, it is provided with a 

 sheath, which lies along the mouth, and the aperture to which is 

 forward, about where the tip of the tongue in the mouths of other 

 animals is when at rest. The snake has no necessity to open its 

 mouth to use this tongue which is in such constant requisition ; a 

 tiny aperture in the upper lip, " a chink in the rostral shield " 

 permits its exsertion and the free play of the sensitive tips. 



Another remarkable peculiarity in snakes is a volitional action 

 of the trachea or windpipe, which can be brought forward beyond 

 the mouth. Though snakes can do for a considerable time without 

 breathing, there are occasions when they require to take fresh 

 breath when it would be impossible to do so; as, for instance, while 

 feeding, when the mouth and throat are completely gorged with 

 their prey. In this case the adjustable windpipe advances, and 

 may sometimes be seen hanging an inch or so out of the mouth, 

 and having at its extremity a sort of lip or valve, very flexible, 

 and opening or closing as the air is drawn in or expelled. This 

 trachea, or air-tube, being also a very delicate organ, and 

 liable to injury through the intrusion of dust, or of particles of 

 fluff, etc., from the prey which is being swallowed, can be opened 

 or closed at will by this mobile valve at its entrance. The 

 anterior portion of the trachea lies along the mouth when at rest, 



