1880.] NATURAL SCIENCES OF PHILADELPHIA. 385 



ON THE TEMPORAL AND MASSETER MUSCLES OF MAMMALS. 

 BY HARRISON ALLEN, M. D. 



Systematic writers have described the temporal and masseter 

 muscles in mammals as being distinct from one another. I hope 

 to show that they are, in the great majority of forms, parts of the 

 same muscle. 



I have found in my dissections that the temporal muscle,^ as a 

 rule, has a deep and a superficial set of fibres. The deep set arises 

 from the floor of the temporal fossa, and makes up the greater 

 part of the muscle. Most of the fibres unite to form a tendon, 

 which is inserted upon the apex of the coronoid process of the 

 lower jaw. Many of the fibres which do not so unite are inserted 

 upon the median surface of the coronoid process ; others again are 

 continuous with the superficial fibres. The superficial set of fibres 

 arise from the temporal aponeurosis. It is continuous in the main 

 with the deep fibres of the masseter, and the fibres are inserted 

 upon the lateral surface of the coronoid process. A partially 

 distinct slip arising from the median aspect of the malar bone, 

 and the ridge on the squama over the external auditory meatus, 

 is an accession to the superficial fibres, but possesses a tendency 

 to unite with the fibres of the deep set in the anterior portion 

 of the fossa. These fibres maj^ receive the name of the supra- 

 zygomatic portion of the masseter. They are inserted at the base 

 of the coronoid process, forming a thin glistening tendon within 

 and a little posterior to the anterior border of the body of the 

 masseter. The supra-zygomatic slip is merged with the large 

 superficial mass in the dog. 



I believe that I have detected as part of the general plan of the 

 masseter muscle, when well developed, that it is composed first 

 of a tendino-muscular layer, rising tendinouslj' from the anterior 

 part of the zygoma or the maxilla near the infra-orbital foramen, 

 and is inserted muscularly into the angle ; second, of a nearly 

 vertical laj'er, tendinous below near the angle, muscular near the 

 zygoma ; third, of a nearh' vertical layer, having a disposition to 

 become tendinous, both near the angle and at the malar bone ; 

 fourth, of a smaller laj-er occupying the fossa on the lateral 

 surface of the ramus, and which exhibits a glistening laj'er of 



1 For convenience the temporal and masseter will be held as distinct in 

 the descriptions. 

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