388 



PROCEEDINGS OF THE ACADEMY OF 



[1880. 



Fig. 1. 



masseteric fibres. It joins the superficial fibres on a line with the 

 coronoicl process. The decn fibres furnish a brilliant tendon, 

 which extends forwards quite to the orbito-tcmporal septum; 

 thus differing strikingly from the arrangement in man. The deep 

 fibres are further seen to be imperfectly^ difterentiated from the 

 internal pterj^goid muscle. 



The masseter muscle is composed of the following: — 1st. A 

 layer arising aponeurotically from the anterior third of the zygo- 

 matic arch, and pissing obliquely downward and backward to the 

 angle. 2d.- A k , er resembling the foregoing ; it arises from the 

 zygomatic arch at its middle. The fibres are nearly vertical and 

 end tendinously at the angle. 3d. A layer arising tendino- 

 muscularly from the posterior third of the zygomatic arch. Its 

 fibres are inserted upon the upper half of the ascending ramus of 



the lower jaw. These layers merge 

 anteriorly ; indeed, are indistin- 

 guishable at the anterior border. 



In the dog the superficial fibres 

 are much better developed than in 

 either the macaque or man, and 

 cover in the deeper fibres, while thej' 

 do not form at an}' part a supra- 

 zygomatic slip ; the general ar- 

 rangement of both temporal and 

 masseter muscles as in other mam- 

 mals. The masseter exhibits six 

 cleavages, of which the last or 

 deepest occupies the fossa on the 

 outer surface of the ramus, and is 

 directly continuous with the super- 

 ficial fibres of the temporal (fig. 1). 

 In the coati, Nasua narica^ the 

 superficial fibres, as in the dog, 

 completely conceal the deep fibres. 

 The supra-zygomatic slip is beauti- 

 fully distinct. Branchesof a con- 

 spicuoas venule which can be seen 

 lying upon the superficial portion 

 disappear abruptl}' as they appi'oach the upper border of the 

 supra-zygomatic slip. Subsequently dissection detects the trunk 



Transverse section through masseter and 

 temporal muscles (one inch behind the 

 eye), Canis familiar is. 



X, Superficial temporal fibres. 



XX, Deep temporal fibres. 



XXX, Superficial masseteric fibre, sepa- 

 rated from A' by a tendinous sheet. 



XXXX, Internal pherygoid muscle, cut 

 transversely. 



