116 



HITCHCOCK'S ANATOMY 



trie fibres, And the antagonists are those muscles which are 

 inserted into it, coming from the different bones of the face 

 moving the lips and nostrils, and giving much of the expres- 

 sion of emotion in the countenance. 



238. Masseter and Temporal Muscles. — The elevators of 

 the lower jaw are two : the Masseter (chewing) and the 

 Temporal (from the bone on which it lies). They are at- 

 tached to the posterior portion of^the bone near the joint, since 

 if their position was nearer to the front part of the bone they 

 would not contract sufficiently to bring the jaws together. 



239. Digastric Muscle. — The lower jaw is carried down- 

 wards by the Digastricus (two bellies) muscle. This is a long 

 round muscle like a cord, which commences just below the 

 lower front teeth, and from thence runs downwards and back- 

 wards to the os hyoides, where it runs through a tendinous 

 loop ; after this it passes upwards and backwards to the mas- 

 toid process upon the temporal bone, just behind the ear. 

 The contraction of this muscle then will open the mouth, when 

 the os hyoides is made fast ; but if the jaw be confined by 

 its elevator muscles, the os hyoides will be the movable por- 

 tion, and will be elevated. The necessity of such an arrange- 

 ment is evident from the fact, that no muscle from the jaw to 

 the hyoides would be of sufficient length to open the lower 

 jaw by its contraction ; and if it were to run backwards to 

 the spinal column, the violence with which it must contract 

 to accomplish its object, would produce such pressure upon the 

 vessels and nerves of the neck as to injure them. 



240. Slerno-Clcido-Mastoideus. — A bow, or bending of 

 the head upon the spinal column, is effected by the action of 

 the Sterno-Cleido-Mastoideus muscle (named from its attach- 



What are its antagonists? What muscles aid very much in giving expression to tho 

 countenance ? 23S. What arc the two pairs of muscles that bring the jaws together in 

 the act of chewing ? 239. State the muscle that opens the mouth. What mechanical 

 peculiarities in its structure and operation ? Why the necessity of such a complicated 

 arrangement? 240. What is the muscle by whose action wo bow the head? * 



