42 ANATOMY OF THE RAT 



External part. Origin. It is attached anteriorly to the 

 skull in an elongated pit ventral to the base of the zygo- 

 matic process of the maxillary bone. From here a strong 

 flat tendon passes backward over the outer surface of the 

 internal part of the muscle. It originates posteriorly from 

 the posterior half of the zygomatic arch. The anterior and 

 posterior regions blend posteriorly vvdth one another and 

 with the internal part. Insertion, the mandible. 



This muscle is a powerful elevator, raising the lower jaw. 

 The anteroposterior fibers, especially of the external part, 

 presumably draw the jaw forward in gnawing. 



Temporal Muscle. This is a powerful muscle occupying 

 the posterior part of the orbito-temporal fossa and the side 

 of the head behind it. Origin : the temporal line, the post- 

 tympanic hook, the lateral surfaces of the parietal and 

 squamosal bones, and the posterior wall of the orbito- 

 temporal fossa. Insertion: the coronoid process and the 

 other parts of the mandible. It elevates the lower jaw. 



The Quadratus Laibii Superiork Muscle is a triangular 

 structure whose apex is at the anterodorsal angle of the 

 orbito-temporal fossa; it is inserted at its broad end into 

 the whisker pad. 



SUPERFICIAL MUSCLES OF THE NECK, SHOUL- 

 DER, AND UPPER FORE LIMB (LATERAL VIEW) 



Levator Auris Longus Muscle. It extends from the mid- 

 dorsal line of the neck as far forward as the back of the 

 head, to the base of the auricle of the ear. It pulls the 

 auricle dorsocaudad. 



Acromiotrapezius Muscle. Origin, the spines of all the 

 cervical and first four thoracic vertebrae. Insertion: (1) 

 the clavicle; (2) the acromion process and lateral edge of 

 the spinous process of the scapula. 



Clavotrapezius Muscle. Origin, the medial half of the 



