LIPS IN THE SHEEP. 139 



Lips. The lips in the sheep are of the same structure as in 

 the horse and in the ox muscular within, the muscular fibres 

 being enclosed between skin and mucous membrane. In the 

 mucous membrane glandular bodies are imbedded, which pour 

 forth a peculiar secretion to mingle with the saliva. The 

 muscles of the lips and mouth in such animals as the sheep 

 differ considerably from the corresponding muscles in man. 

 The orbicular muscle, or sphincter of the mouth, is very thick, 

 but is small comparatively. The common levator of the ala 

 of the nose and of the upper lip is confounded with the 

 proper levator of the upper lip. The levator of the angle of 

 the mouth, small and elongated, descends almost vertically 

 from above and behind, downwards and forwards. The 

 zygomatic muscle, long and thick, but narrow, arises by a 

 long and narrow tendon. The buccinator, or alveolo-labial, 

 which is of great thickness, is much elongated. The depres- 

 sion of the lower lip is not determined by proper muscles, but 

 is accomplished by a very thin portion of the cutaneous 

 muscle (platysma myoides), which passes over the buccin- 

 ator, to become confounded with the orbicular muscle of the 

 lips. The temporal muscle, notwithstanding its important 

 use in mastication, though thick, is very small. The mas- 

 seter is very large and of moderate thickness : it consists 

 of two layers, . the external being highly tendinous ; the 

 internal small, and of a triangular form. The internal 

 pterygoid is long, broad, and of medium thickness; the ex- 

 ternal pterygoid is very thick and of moderate length, passing 

 in a transverse direction. The digastric is small : its anterior 

 belly is very much larger than its posterior, and is attached 

 to the posterior third of the lower jaw. In the ox there is a 

 square muscle extended from one digastric to the other. The 

 lips are much u'sed by sheep in grazing the pasture. 



Cheek. The buccinator, or alveolo-labialis, is the muscle 



