Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/56

42 External part. Origin. It is attached anteriorly to the skull in an elongated pit ventral to the base of the zygomatic 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 Superioris 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.

Levator Auris Longus Muscle. It extends from the middorsal 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