94 MUSCULAR SYSTEI\i. 



Relations. — Externally, with the skin ; internally, with adi- 

 pose tissue, the labial glands, and the membrane of the mouth. 



Direction. — Semicircular, in the horizontal line. 



Structure. — Consists of two bands of fleshy fibres, the upper 

 one of which is broader, thicker, redder, and stronger than the 

 lower. 



Action. — To approximate the lips and retain them in contact; 

 also to assist in the dilatation of the nostrils. 



6.— ANTERIOR MAXILLARY REGION, 

 Comprising the muscles whose office it is to move the lower jaw. 



TEMPORALIS. — Temporo-maxiUaris. 



Situation. — Upon the parietal and temporal bones. 



Form. — Convex, externally ; concave, internally: broad, above; 

 narrow and convergent, below. 



Attachment. — Superiorly, to the vertex and the anterior occipi- 

 tal bone ; to the convex surface of the parietal ; to the squamous 

 plate and zygomatic process of the temporal bone ; and to a small 

 portion of the frontal : inferiorly, to the coronoid process of the 

 inferior maxilla. 



Relations. — Externally, with the attollentes aurem and the zy- 

 goma; internally, with the cranial bones ; postero-externally, with 

 the ear ; anteriorly, with a volume of fatty substance lodged at the 

 back of the orbit. 



Direction. — From behind, forwards ; and from above, down- 

 wards : the fibres taking a curvilinear course. 



Structure. — Covered by a dense aponeurotic expansion, deno- 

 minated the temporal faschia ; the broad part of the muscle is 

 fleshy, but is intersected horizontally through its middle by a 

 layer of tendon. Below, it is tendinous in its attachments to the 

 sharp edges of the coronoid process; but fleshy around the sides 

 of it. 



Action. — To raise the lower against the upper jaw ; and, 

 thereby, when the mouth is opened, to shut it again. It is one 

 of the principal agents in manducation. 



MAssETER. — Zygomatico-maxillaris. 



Situation. — It forms the prominence of the cheek. 



Form. — Broad, thick, semi-oval: superior and anterior sides, 

 rectilinear ; postero-inferior border, curvilinear. 



Attachment. — Superiorly, to the whole of the zygomatic ridge, 

 and lower border of the arch, reaching as far back as the mastoid, 

 process ; inferiorly, to the roughened border surrounding the angle 

 of the jaw, and to the contiguous parts of the external surface. 



