MYOLOGY 27 



entirely covered by, the levator labii. It is a very slender 

 muscle arising from a slight fossa upon the dorsal part of 

 the zygomatic process of the maxilla. It quickly becomes 

 tendinous and is inserted upon the lateral side of the 

 anterior nasal opening. 



M. sternofascialis (fig. 7) occurs in Homodontomys 

 only as a slender slip arising from the midventral line at 

 the posterior end of the manubrium. It extends caudo- 

 dorsad beneath the platysma and disappears in the fascia 

 covering the parotid gland. It constitutes a remnant of 

 what is often called the deep panniculus, or in certain 

 mammals, the sphincter colli profundus. 



In neither JSfeotorna nor Teonoma could a trace of this 

 muscle be found. 



The innervation of the superficial facial musculature is 

 by the N. faciahs. 



II. Masticatory musculature 



In rodents the chief muscles of mastication are divisible 

 in varying degree, but they had best be treated as occurring 

 as parts of four, main muscles, as follows: 



Mm. masseter pterygoideus externus 



temporalis pterygoideus internus 



In addition, the digastric is an important masticatory 

 muscle in most if not all rodents, but this had best be 

 placed elsewhere. 



M. masseter is divisible, with more or less ease, into 

 three main parts, comprising the following: 



Pars superficialis (figs. 5, 7, 23, 24, 25), having origin 

 by a heavy tendon from the slight process immediately 

 cranio-ventrad to the infraorbital foramen. The tendon 

 broadens to form a tough aponeurosis covering all the 

 lateral belly of the muscle excepting its extreme posterior 

 portion. The muscle fibers take origin chiefly from the 



