176 THE VITAL FUNCTIONS. 



vegetables ; for in these the glands are more con- 

 siderable.* In Fishes there is no structure of this 

 kind provided, there being no mastication per- 

 formed ; and the same observation applies to the 

 Cetacea. In the cephalopodous and gastero- 

 podous Mollusca, we find a salivary apparatus 

 of considerable size: Insects, and the Annelida,'^ 

 also, generally present us with organs which 

 appear to perform a similar office. 



The passage of the food along the throat is 

 facilitated by the mucous secretions, which are 

 poured out from a multitude of glands inter- 

 spersed over the whole surface of the membrane 

 lining that passage. The Camel, which is formed 

 for traversing dry and sandy deserts, where the 

 atmosphere as well as the soil is parched, is spe- 

 cially provided with a glandular cavity, placed 

 behind the palate, and which furnishes a fluid 

 for the express purpose of moistening and lubri- 

 cating the throat. 



In the structure of the (Esophagus, which is 

 the name of the tube along which the food 

 passes from the mouth to the stomach, we may 

 trace a similar adaptation to the particular kind 

 of food taken in by the animal. When it is 

 swallowed entire, or but little changed, the 



* The large salivary gland in the woodpecker, is seen at s. 

 Fig. 271, page 132. 



t The bunch of filaments, seen at s, Fig. 260 (p. 103) are 

 the salivary organs of the leech. 



