OF DIDELPHYS VIRGINIANA. 93 



and the zygoma, and extends upon the cranium, beneath the temporal fascia, so far as 

 to overlie the greater portion of the temporalis. It has extensive origin from the 

 greater part of the temporal fascia, sometimes as high up as the parietal crest ; from the 

 stout fibrous band between the malar and supraorbital protuberance that defines the back 

 part of the orbit, from the lower part of the occipital crest and the squamosal ridge, and 

 from the whole of the inner surface of the zygoma. This temporal or cranial portion of 

 the masseter is inserted into the whole of the outer surface of the broad coronoid plate. 

 The masseteric portion proper, or that hnng below the zygoma, arises not only from 

 the lower border of the latter (being directly continuous with the above), but also, and 

 chiefly, by a very stout tendon from the most anterior and lowest part of the malar. 

 While the former portion is flattened and more or less fan-shaped, its fibres converging 

 from the broad origin above described, the latter is a thick bulging mass, the general di- 

 rection of the fibres of which is backward as well as downward. This prominent bundle 

 overlaps the margin of the jaw, extends to the inner edge, and is inserted into the whole 

 of the broad, triangular, flat space, meeting the lower border of the internal pterygoid. 

 It reaches along the jaw, from the anterior margin of the last named muscle, to the inner 

 hamular process of the mandible. The anterior border of the masseter is blended with 

 the corresponding part of the temporalis. 



TemjwraUs. — On reflecting the masseter, this muscle is seen filling the remainder of 

 the cranial depression, separated from the foregoing (except along its anterior border) by a 

 thick, stout aponeurosis, that forms the true tendon of the temporalis, radiating from the 

 apex of the coronoid much as in the human subject. The periphery of the muscle corres- 

 ponds to the contour of the temporal fossa ; it takes origin from the occipital, parietal and 

 frontal crests, and all the subjacent bones ; it is inserted, tendinous, into the top of the cor- 

 onoid, and fleshy, into the greater part of the inner surface of the same process, which is 

 thus completely embedded in muscle. The temporal is thinner and weaker than the mas- 

 seter, as well as of less superficial extent ; but as already stated, the two are completely 

 blended in some portions, and must always act consentaneously. 



Pterygoideus internus. — ^Like the foregoing, this muscle is of great size and poAver, well 

 deserving the name of " internal masseter" (Winslow), sometimes applied to it in anthro- 

 potomy. Its line of traction is such that it has little or no effect except in direct closure 

 of the jaws. It forms on the inside of the ramus of the jaw a prominently convex bundle, 

 corresponding in extent with, and yielding but little in size to, the masseter. It arises 

 fleshy from the sphenoidal pterapophysis, contiguous part of palatal, and the whole of the 

 pterygoid, which slender little bone projects downward into and is buried in the fleshy 

 mass. Enlarging and bulging as it descends, it is inserted fleshy into the inner surface of 

 the mandibular ramus, from the termination of the temporalis to the margin of the bone, 

 and along the latter from the hamular process as far as the anterior margin of the masse- 

 ter. It completely fills the depression between the incurved process and the articular head 

 of the bone. 



Pterygoideus externus. — The disparity in size between this and the preceding muscle is 

 very striking ; the external pterygoid being, as it were, reduced to its simplest expression. 

 It is a very small conical, or pyramidal muscle, and is not divisible, as in the human sub- 

 ject, into two " heads," or parts. It arises fleshy from the alisphenoid, near the median 

 line of the bone, close by the foramen rotundum, and proceeds, narrowing, almost directly 



MEMOIRS BOST. BOO. NAT. HIST. VOL. II. 24 



