26 ANATOMY OF THE WOOD RAT 



the fore part of the cranium between the ears and eyes, 

 and merge partially with fibers of the orbicularis oculi 

 and auriculo labialis. 



M. orbicularis oculi (figs. 4, 23, 24) originates from 

 the frontal bone immediately mediad of the lachrymal, 

 and is poorly developed. Its fibers surround the eye, and 

 some of them merge with those of both the interscutularis 

 and levator labii. 



M. orbicularis oris (fig. 4) is with difficulty separable 

 from the tough tissue about the lips, especially in Homo- 

 dontomys, and is rather poorly developed in the genus. 



M. buccinatorius (figs. 5, 23, 24). This thin sheet of 

 muscle has origin from the portion of the premaxilla and 

 maxilla along the curve formed by the root of the incisor 

 from near its alveolus almost to the infraorbital foramen 

 directly ventrad to the origin of the infraorbital slip of the 

 masseter. Passing ventrad, the fibers upon its superficial 

 belly develop noticeably into striated fat cells, and the rest 

 of the muscle passes insensibly into the mucous membrane 

 of the cheek, and thus to the orbicularis oris. A small por- 

 tion of the muscle, similarly inserted, also has connection 

 with the tissue overlying the diastema of the mandible. 

 This muscle is often classed with the masticatory group, 

 but in rodents it plays but little part in actual mastication. 



M. auriculo labialis (zygomaticus) (fig. 4) is a slender 

 band of muscle extending from the orbicularis oris, at the 

 corner of the mouth, across the cheek, with insertion at the 

 base of the cartilage of the ear. A few of the dorsal fibers 

 may be continuous with the interscutularis. 



M. levator labii (figs. 4, 23, 24) is well defined, es- 

 pecially in Neotoma. Origin is along the lateral margin 

 of the ascending branch of the premaxilla for some 7 mm., 

 extending cranio-ventrad in a fan-wise manner to an in- 

 sertion upon the fibrous, mystacial pad. 



M. dilator naris (figs. 5, 23, 24) lies deep to, and is 



