ANATOMY OF THE IIORSE. 
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m a s s et e r .—Zygomatic o-maxillai'is. 
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 ; interiorly, to the roughened border surrounding the angle 
of the jaw, and to the contiguous parts of the external surface. 
Relations. —Externally, with the panniculus carnosus, cellular 
tissue, and branches of the portio dura; internally, with parts of 
the superior and inferior maxillae, buccinator, mass of yellow Tat 
filling the intermaxillary vacuity, posterior and anterior masseter 
arteries and veins; superiorly, with the temporal artery and vein; 
posteriorly, w 7 ith the parotid gland; anteriorly, with the parotid 
duct, anterior maxillary artery and vein. 
Direction. —Oblique: from above, downwards; and from be¬ 
fore, backwards. 
Structure. —Of its exterior, the superior two-thirds is aponeuro¬ 
tic ; internally, it is composed of several distinct fleshy layers, 
separated by aponeurotic intersections. 
Action. —In co-operation with the former muscle, to elevate 
the lower jaw 7 , and maintain it in approximation against the upper. 
STY LO-M AXILLARIS. 
Situation. —Behind the lower jaw 7 . 
Figure. —Pyramidal: base turned downwards and forwards. 
Attachment. —Superiorly and posteriorly, styloid process of the 
occipital bone: inferiorly and anteriorly, angle of the low T er jaw. 
Relation. —Externally, with the parotid gland, temporal and 
occipital branches of the jugular vein, and the arteries piercing the 
gland; internally, with the membrane bounding the guttural ca¬ 
vities ; superiorly, with the stylo-hyoideus. 
Direction. —Oblique : from behind, forwards ; and from above, 
downwards. 
Structure. —Tendinous, at its occipital attachment; remainder 
fleshy, intersected with layers of tendon, and having aponeurotic 
stripes along its surfaces. The posterior division of the digastri- 
cus is inseparably united with the inferior border. 
Action. —To draw the jaw backward, and at the same time 
depress it: it therefore assists in opening the mouth, and so far 
is an antagonist to the two former muscles. 
p teryg o i d e us internus.— Spheno-maxillaris. 
Situation. —The same relative position upon the inner side of 
the jaw to w 7 hat the masseter has upon the outer, filling up the 
excavation there in the bone. 
