1880.] NATURAL SCIENCES OF PHILADELPHIA. 395 



masseter will be found to be variable. The parts in the masseter 

 of the Virginian deer ( Gariacus virginianus) presented essentially 

 the same features as in the calf. The superficial layer of the tem- 

 poral resembles that of the calf, but the main tendon is small and 

 is without muscular fibres, as it lies behind the orbito-temporal 

 septum. The suiDerficial portion is small. It lies behind the 

 coronoid, in the posterior superior portion of the temporal fossa. 



It must be said that the human anatomist seems warranted in 

 treating the masseter and temporal muscles distinct. Quain, in- 

 deed, affirms that some of the posterior temporal fibres arising 

 from the temporal fascia blend with the deep fibres of the masse- 

 ter, but the union of the muscles in man is a rare anomalj^ 

 Macalister (Muscular Anomalies in Human Anatomy. Trans, 

 of the Roj^al Irish Academy, xxv, 1872, 18.) has met with it 

 but once. I have seen it once onl3\^ No mention is anywhere 

 made of the presence of the supra-zygomatic slip. It is quite- 

 likel}' that it maj' be occasionally seen in the cellulo-adipose tissue 

 above the zygoma. Of the presence of any peculiarities in the 

 anthropoid apes in these muscles I am uninformed. 



The arrangement of the superficial layerof the temporal muscle 

 in man is ver}^ similar to that seen in the quadruped. This layer 

 arises from the temporal aponeurosis, and while thin posteriorly 

 is thick anteriorly, behind the orbital septum. If this layer of 

 fibres be divided posteriorly and the anterior portion turned for- 

 ward, a thick radiated tendon is displayed beneath. This is the 

 tendon of the deep set of fibres which here as in quadrupeds 

 constitute the mass of the muscle. The fibres of the superficial 

 and deep sets are continuous behind the orbital septum. This 

 method of displaying the temporal muscle has been for many 

 years employed b}' Prof. Joseph Leidy in his demonstrations at 

 the University of Pennsylvania. 



From the above examination I have come to the following con- 

 clusions : — 



(1) While it is convenient to separate these muscles it must be 

 remembered that in many mammalia the tendency is for the mas- 

 seter and temporal muscles to unite-^the deep part of the former 

 being continuous with the superficial part of the latter. 



1 In a dissection of the muscles in a mulatto child at term, I found the 

 deeper plane of masseteric fibres arising from the external surface of the 

 temporal tendon. 



