96 MUSCULAR SYSTEM. 



Re/a(lo)i. — Externally, with the branch of the jaw, and poste- 

 rior maxillary nerve and blood-vessels ; internally, with the digas- 

 tricus, hyoideus, stylo-pharyngeus, the os hyoides, the larynx, 

 the anterior portion of the parotid gland, the submaxillary vessels, 

 and the ninth and recurrent nerves : anteriorly, with the mylo- 

 hyoideus and gustatory nerve; posteriorly, with the parotid gland, 

 guttural cavities, and the next muscle : superiorly, with the base 

 of the cranium; inferiorly, with the stylo-maxillaris and the skin. 



Direction. — Divergent, from above, downwards. 



Structure. — Fleshy, plenteously intersected with tendon. 



A ctioii. — To raise the jaw. If one act alone, the jaw, in being- 

 closed, will be drawn to one side : the alternate action of the two 

 produces the lateral movement of the jaw which is so effectual in 

 comminuting the food. 



PTERYGOIDEUS EXTERNUS. 



Situation. — Above and behind the former. 



Form. — Short, thick, cylindrical. 



Attachment. — Anteriorly, to the ala and crus of the sphenoid; 

 posteriorly, to the roughened depression upon the inner side of 

 the jaw, at the root of the condyle. 



Relation. — Anteriorly, inferiorly, and internally, with the pre- 

 ceding muscle, and the posterior maxillary nerve; superiorly, 

 with the orbit; posteriorly, with the articulation of the jaws ; ex- 

 ternally, with the neck of the jaw. 



Directio)i. — Oblique: from behind, forwards; and from with- 

 out, inwards. 



Structure. — Fleshy, with slight tendinous intersections. 



Action. — To assist in the elevation of the jaw; and, at the same 

 time, to draw it forwards : it is the antagonist in particular of the 

 stylo-maxillaris. 



6.— HYOIDEAL REGION. 



The muscles in this region, and those remaining to be described, 

 belonging to the head, are comprehended within the inter-max- 

 illary space — between the branches of the lower jaw. 



DiGASTRicus. — Portiou of the Sti/lo-maxillaris. 



Situation. — Along the inner side of the lower jaw. 



Form. — Broad and flattened at the extremities; cordiform in 

 the middle. 



Attachment. — Posteriorly, to the styloid process of the occipi- 

 tal bone ; anteriorly, to the side of the jaw, midway between the 

 angle and the symphysis. 



Relation. — Externally, with the jaw and pterygoidei ; inter- 



