132 INTRODUCTION. 



general, however, the lips of the Carnivora are of no avail as organs for 

 the prehension of food. The true Cetacea have marginal lips only, 



Among the aquatic Pachydermata, the Duyong has the muzzle broad 

 and flat ; and the sides of the upper lip are garnished with short, thick, 

 wiry bristles : it feeds upon the submarine algae and fuci, which grow upon 

 the rocks of the Indian seas ; but the extent to which it uses its upper 

 lip is not ascertained : most probably, its voluminous tongue, the surface 

 of which is covered with long villous papillae, is of important service. 

 The wiry bristles of the upper lip are, doubtless, feelers. 



Leaving this discursive review of the tongue and lips, it may be ob- 

 served, as a general rule, that the food of all Mammalia, whatever it may 

 be, when taken into the mouth, is not swallowed without the addition of 

 certain fluids, afforded by various glands, in which it is secreted : of these 

 fluids, the principal is the saliva. The glands, ih which this fluid is elabo- 

 rated, are several ; namely, the parotid, placed before the ear, and at the 

 back of the articulating branch of the lower jaw ; the submaxiilary, 

 placed at the inner side of the posterior angle of the lower jaw ; and 

 the sublingual, placed at the root of the tongue. Besides the saliva, a 

 mucous fluid is furnished, from numerous crypts in different parts of 

 the cavity of the mouth. The use of the saliva,* or, rather, one of 

 its uses, is to moisten the food previously to its being swallowed. In 

 herbivorous animals, as the Ox, which grind their food to a pulp, the 

 salivary glands are very large, and secrete abundantly : the process of 

 chewing excites their elaborative action, and they supply their fluid in the 

 requisite quantity. Even the appearance of food, placed before an 

 animal in a state of hunger, causes a flow of saliva. When the general 

 system is diseased, or labouring under fever, the action of the salivary 

 glands is suspended, the mouth is dry, and the tongue parched with 

 thirst. Duly prepared, then, by the teeth, and moistened with saliva, the 

 food, by means of the action of the tongue and muscular wall of the 

 pharynx, is passed into the oesophagus, or tube leading into the stomach. 

 The oesophagus is muscular, its parietes, which consist of longitudinal 

 and of circular fibres, forming a tunic of considerable thickness : inter- 

 nally, it is lined with a smooth membrane, lubricated by a mucous fluid, 

 poured out from crypts dispersed over it. In the herbivorous Mammalia 

 it is narrower than in the Carnivora. In some herbivorous animals 

 the fauces, forming the back of the mouth, are funnel-shaped, opening 

 into the oesophagus, through a small orifice, surrounded by a sphincter 

 muscle of circular fibres, allowing only of the gradual transmission of 

 food, which has been previously reduced to a thorough pulp. The 



* The saliva, besides tempering the food, moistens the mouth, and renders the action of the tongue 

 free and precise : in addition to which, according to M. Donne, it neutralizes, by the free alkali it con- 

 tains, the excess of acid in the gastric juice, in the intervals between digestion. 



