DIGESTIVE SYSTEM. 



OF THE MOUTH. 



It may be observed here (as preparatory 

 to the description of this part), that, in 

 quadrupeds in general, the facial angle is 

 one of very considerable obliquity, in con- 

 sequence of the prolongation of that part 

 of the head which corresponds to the face 

 in the human subject; and this develop- 

 ment of feature is in none more strildna: 

 than in the horse and dog. Consequently, in 

 these animals, the nose and mouth are 

 cavities of large dimensions. And in the 

 horse, the mouth appears to have been thus 

 prolonged, not only to enable him to col- 

 lect his food with more facility, but also 

 that he might subject greater parcels of it 

 at a time to the action of the grinding 

 teeth, whereby the processes of mastication 

 and deglutition are greatly accelerated. 



" Conformation. — The mouth is con- 

 structed in part of bone, and in part of 

 soft materials. The superior and anterior 

 maxillary and the palate bones form the 

 roof; the inferior maxilla, the lower part; 

 the incisive teeth, the front ; and the 

 molar teeth, the sides. The lips, cheeks, 

 soft palate, gums, and buccal membrane, 

 constitute its soft parts. The tongue occu- 

 pies its cavity, and the salivary glands are 

 appendages to it. 



"lips. 



" General Conformation. — The lips, two 

 in number, superior and inferior^ are at- 

 tached to the alveolar projections of the su- 

 perior and inferior maxilla3, by the muscles 

 that move them ; by the cellular tissue en- 

 tering into their composition ; and by the 

 membrane that lines them. Their borders 

 surround and bound the orifice of the 



mouth, and are united together on either 

 side ; which points of union are denomi- 

 nated their commissures, or the angles or 

 corners of tlie mouth. Exteriorly, the lips 

 are creased down the middle by perpen- 

 dicular lines of division ; exhibit little 

 papillary eminences upon their sm-face ; 

 and present a softer and shorter coating of 

 hair than what is found in ordinary places, 

 out of which project several long sti*aggUng 

 horse-hairs or ivhiskers. The inferior lip 

 is altogether smaller, and is thinner in sub- 

 stance, than the superior ; and is distin- 

 guished by a remarkable prominence about 

 its centre, from which gi'ows a tuft of long 

 coarse hairs, vulgarly designated as the 

 beard. 



" Structure. — The lips are both muscu- 

 lar and glandular in their composition. 

 Several small muscles,* arising from the 

 maxillary bones, are inserted into them, and 

 endow them with great self-mobility : one 

 alone, consisting of circular fibres, is inter- 

 woven in their substance without having 

 any other connection ; this is denominated 

 the orbicularis oris, or sphincter labiorum, 

 from its use, which is that of closing the 

 mouth. This muscle is an antagonist to 

 all the others ; they raise or depress the 

 lips, or draw them to one side ; but this 

 contracts them, and occasionally projects 

 them in such a manner that the horse can 

 exert with them a prehensile power, which 

 is most remarkably evinced at the time that 

 he is picking up grain from a plain sm'face ; 

 indeed, the act of nibbling our hands with 

 his lips demonstrates this faculty, and also 

 the force with which he can employ it. The 

 lips are lined by the same membrane that 

 lines other parts of the cavity of the mouth. 



* PercivaH's Hyppopathology. 



(88) 



