Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/55

Rh Great care should be exercised to avoid removing the cutaneous muscles, which are located immediately under the skin. The student should be provided with two rats, one for the study of the muscles, the second for the dissection of the remaining soft parts. Only the larger superficial muscles are included in the following account.

The cutaneous maximus muscle spreads out fanwise from the region of the arm pit. It covers the back from the shoulders to tail, the sides of the trunk posterior to the front leg, and a large part of the ventral surface of the trunk. Its function is to move the skin, in which it is inserted.

The platysma is a thin sheet of muscle which radiates from the posterior angle of the mouth, covers the posterior side of the face and the lateral surface of the neck, and sends a branch up in front of the ear. The broad cervical portion is attached along the middorsal line of the neck.

Exercise X. Sketch the cutaneous maximus and platysma muscles into an outline drawing of the lateral view of the rat.

Carefully remove the two preceding muscles.

Masseter. This muscle consists of two main parts, an external and an internal. Anteriorly these two are distinct, but they blend posteriorly.

Internal part. Origin, the whole length of the zygomatic arch. Insertion, the mandible, posterior to the diastema. Anteriorly the fibers run nearly at right angles to the long axis of the jaw ; posteriorly they form an acute angle with this axis.