1901.] TIIE MUSCLE* 01 THE UNol'LAT.V. 665 



Hippopotamida?, Tapiridae, and Elephantidte. Bronn (VI.), pro- 

 bably on tbe authority of Bendz, says that two layers may always 

 be made out in Ungulates, and Chauveau notices the same in the 

 Horse. Our own experience is that these two planes require some 

 little care to display satisfactorily ; and authors such as Miall 

 and Greenwood in the Elephant (XXIX.). and Kinberg in the 

 Chevrotaiu (X.), make no mention of any bilamination, although 

 they have evidently dissected the muscle with care. The temporal 

 never seems to be large enough to meet its fellow in the sagittal 

 line of the skull, although in the Camel (17) the two approach 

 very closely. 



Masseter. — This muscle is always very well developed, and has 

 the usual origin from the zygomatic arch and insertion into the 

 outer surface of the ramus of tlie mandible. 



The chief interest of various writers seems to centre in the 

 number of layers into which the muscle may be divided, and we 

 have no hesitation in saying that these are by no means constant, 

 and probably mean very little. 



h\ the Horse, for example. Bendz and Liesering say there are 

 two lamina 1 , v. Teuteleben three, while Chauveau says that there 

 are several laminae of which two are very distinct. 



In the Ruminants, again, v. Teuteleben says there are three 

 laminae, but Allen says six. 



In the following animals there are two layers which correspond 

 with the arrangement found in man : — Hippopotamus (3), Pig (6), 

 Bed-River Hog (11), Peccary (14), Bed Brocket (27), Mexican 

 Brocket (28), Sheep (43), Mouflon (45), Elephant (74, 77). In 

 the Duiker-bolc (49). Chevrotaiu (21), Hyrax (68), and Tapir (54, 

 55) no lamination was present ; while in the fat-tailed Sheep (43) 

 and Kinberg's Chevrotain three layers were made out, the deepest 

 one being the most posterior. We are therefore inclined to agree 

 with Lesbres, on whose opinions we place a good deal of reliance, 

 that two layers are usually fouud in the masseter of Ungulates 

 but that occasionally the muscle may be trilaminar or unilaminar. 



Pterygoids. — Throughout the Order the internal is a much larger 

 muscle than the external, and arises from the posterior part of the 

 alisphenoid and anterior part of the pterygoid bone as well as 

 slightly from the palate. On their way to be inserted the fibres 

 diverge somewhat, and the muscle, becoming fan-shaped, is attached 

 to the mandible between the angle and the inferior dental canal, 

 but more strongly near the lower border. There can be no doubt 

 that in animals which chew the cud the internal pterygoid acts as 

 a powerful lateraliser of the jaw, and it is noticeable that in these 

 the fibres of the muscle arc directed outwards more than they are 

 in tlic Perissodactyla. Lesbres says that in the Horse, and to a 

 less degree in the Kg, the muscle is bilaminar, but that this is not 

 the case iii the Bovid®. Our own experience does not support 

 this generalization, for neither in the Hed-Kiver Hog (11) nor the 

 Peccary (14) which we dissected did we liud any bilamination; 

 while iii the specimen of i be sheep's masticatory muscles iii 



