MYOLOGY 241 



the horse is situated the so-called prominence of the chin, 

 limited posteriorly by the heard, a depressed region which 

 gives point to the curb of the bridle. 



The prominence, which also exists in the ox, is a fibro- 

 muscular pad which blends with the orbicular muscle of the 

 lips, and receives on its superior aspect the insertion of the 

 two muscles {levator menti) by which it is suspended. These 

 arise, above, on each side of the symphysis of the inferior 

 maxillary bone. They raise the lower lip with force, and 

 they are the agents which, as we can sometimes observe in 

 the horse, make it click against the upper lip, suddenly 

 projecting it upwards. This action sometimes becomes a 

 habit, and its continuance constitutes a vice. 



A corresponding structure is found in the pig and in the 

 carnivora, but in them it does not produce an external 

 prominence such as we have described. 



Buccinator (Fig. 90, 9 ; Figs. 91, 92). — Further designated 

 by the name of alveolo-laUal, this muscle is situated on 

 the lateral portions of the face, in the thickness of the 

 cheeks. It consists of two layers, one superficial and the 

 other deep. 



The deep portion arises from the portion of the alveolar 

 border of the superior maxillary bone which corresponds 

 to the molar teeth, and from the anterior border of the 

 ramus of the mandible. Thence it is directed forwards, 

 passes under the superficial layer, and blends with the 

 fibres of the orbicular muscle of the hps. To this part of 

 the buccinator some authors give the name of molar muscle. 



The superficial portion is formed by fibres which pass 

 from the alveolar border of the superior maxillary bone to 

 the corresponding border of the opposite bone. It is very 

 highly developed in the herbivora. 



This muscle acts especially during mastication ; it serves 

 to press back again under the molar teeth the portions 

 of food which fall outside the dental arch. 



In the pig, the ox, and the horse, a muscle which is con- 

 sidered as supplemental to the buccinator is placed along 

 the inferior border of the latter. 



This muscle, which we describe separately under the names 



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