MUSCLES OF THE FACE AND HEAD 



307 



the tendon, enables the latter to move freely through the former. This is 

 more especially the case in the vicinity of joints, as the knee, hock, and 

 fetlock, where movement is most active. Where tendons play over pro- 

 jecting points of bone or other prominences, a small, round sac lined with 

 synovial membrane is placed between them to facilitate the movement of 

 the one over the other. These are known as synovial bursse. 



MUSCLES OF THE FACE AND HEAD 



The muscles of the face comprise a number of longer or shorter strips, 

 most of which are attached by one extremity to the bones above, and by 

 the other to parts about the lij)s and nostrils below. Those attached to the 



Fig. 371.— Muscles of Horse's Head 



A, Temporalis rauscle. B, Levator palpebrie. c, Orbicularis palpebrarum. D, Suj^ernaso-labialis or 

 Levator labii superioris alajque nasi. E, Supemia.xilo-Iabialis or Levator labii superioris proprius. 

 F, Supermaxilo-nasalis or Dilator naris lateralis. G, Orbicularis oris. H, Mento-l.abialis. i. Maxilo-labialis 

 or Depressor labii iuferioris. J, Zygomaticus. K, Buccinator. L, Parotid duct. M, Masseter muscle. 

 N, Parotid gland, o, .Jugular vein. P, Mastoido-humeralis muscle. 



former are for the most part muscles of prehension, and serve to gather up 

 the food and retain it in the mouth during mastication. With one or two 

 exceptions the muscles of the face are arranged in pairs, one being on one 

 side and the other on the other. 



AVhen in action some of them draw the lips upwards, others acting in 

 an oppo.site direction pull them downwards, hence they are called levators 

 and depressors respectively. 



The orifice of the mouth is acted upon by a single muscle that 

 encircles the lips (orbicularis oria), and when in action diminishes 



