HIGH SCHOOL ZOOLOGY. 157 



represented in the lower forms. The hinder part of the roof of 

 the mouth likewise is contractile, and becomes the soft palate, 

 a flap of which, known as the uvula, hangs down in the middle 

 line, so as to cut off a posterior chamber or pharynx from the 

 true mouth-cavity. The aperture between the two is further 

 narrowed by folds at either side, the pillars of the fauces, 

 between which are the tonsils belonging to the lymphatic 

 system. (I, 63). The pharynx communicates above with the nasal 

 cavities, below with the larynx and oesophagus, the aperture 

 into the former tube being always protected by the epiglottis, 

 a movable fold behind the base of the tongue. The primitive 

 mouth-cavity which we studied in the lower forms is thus not only 

 separated into a respiratory chamber above (the nasal cavities), 

 but into an alimentaiy chamber below, which further presents 

 from before backwards, a buccal cavity between the lips and 

 the gums, the mouth-cavity proper and the pharynx. The 

 structural advance which we thus see in the mammals is partly 

 determined by the use of the lips for prehension, partly by the 

 longer retention of the food in the mouth, for admixtui-e with 

 the secretion of the salivary glands, for mastication and for sub- 

 mission to the organ of taste. 



13. In all mammals the salivary glands are arranged in three 

 masses, parotid, submaxillary, and sublingual, and their secretion 

 partly serves to facilitate the swallowing of the food, and partly 

 to aid in the digestion of the starchy constituents thereof The 

 organ of taste is composed of certain bud-like structures which 

 recall the sense-organs of fishes (I, 9), and which are chiefly 

 situated in the walls of trenches surrounding the lai-ge circum- 

 vallate papillse at the back of the tongue. Fungiform and 

 filiform papillae are also present in the tongue of all mammals, 

 the latter clothed with horny epidermic sheaths in the carni- 

 vores, and giving the front of the tongue its rasjj-like surface. 



14. In the lower forms studied, the coelom is an undivided 



