CAVITY OF THE MOUTH. 193 



THE CAVITY OF THE MOUTH. 



This cavity in the horse forms all that extensive opening 

 from the level of the e^^e to the incisor teeth. The mouth 

 is composed of external and internal parts ; the external 

 are the lips and cheeks ; the internal are the gums, the 

 bars, the teeth, the alveolary edges, the palate, and the 

 tongue. The lips form parts of the mouth, and are two in 

 number ; an upper and lower ; each being composed of 

 fleshy masses which extend around the opening to the 

 mouth ; but principally a circular one is apparent, forming 

 the orbicularis oris : the rest are composed of the nume- 

 rous muscles that influence the various movements of the 

 mouth and lips. 



The RETRACTOR ANGLiORis (Plate II. where it is shown 

 turned back) is a portion of the panniculus, and as such has 

 a general action, but no special power over the mouth. The 

 ZYGOMATicus (Plate II. 4) runs from the zygomatic process 

 to, and is the true retractor of, the angle of the mouth. 

 The LEVATOR ANGLIORIS (Plate II. 1) which draws the 

 mouth upward and backward, pulls the upper lip also in 

 the same direction ; and at the same time partially expands 

 the nostril ; arises from near the inner canthus of the eye ; 

 and is inserted into the angle of the mouth, and into the 

 cornua of the nasal cartilages ; forming a loop anteriorly, 

 through which passes the retractor labii superioris. 



Retractor labii superioris (Plate II. 3) pulls back- 

 ward the side of the upper lip ; and also dilates the false 

 nostril. Originates. From the upper jaw upon the outer 

 side, and just before the termination of the zygomatic spine. 

 Inserted. Into the false nostril, and blends with the muscu- 

 lar fibre of the upper lip. 



Levator labii superioris (Plate II. 2), a pair of well- 

 defined muscles, one on either side of the face ; joining in 

 a common tendon, which at length expands and goes to 

 the upper lip ; originating from the junction of the supe- 

 rior maxillar and molar bones. The two would obviously 

 elevate the upper lip ; or one would pull the lip to one 

 side. To the lower lip there are the retractor labii 

 iNFERioRis (Plate II. 7), a well-marked muscle, originating 

 near to the margin of the lower jaw ; and going by tendons 



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