1916] Holliger: Anatomical Adaptations in the Pocket Gopher 463 



cephalad to be inserted in the dorso-caudal angle of the pouch. 

 The function of this muscle is to support and elevate the rear end 

 of the pouch. The retractor of the pouch is a long, band-like 

 muscle which arises from the spinous processes of the last thoracic 

 and first two lumbar vertebrae and the supraspinous ligament, 

 and passes cephalad and ventrad over the shoulder, to be inserted 

 into the whole of the caudal end of the pouch. Its action, as 

 expressed by its name, is to retract the pouch. There is also a 

 ventral retractor of the cheek pouch (not shown in fig. M). This 

 arises from the manubrium of the sternum and passes laterad and 

 cephalad, to be inserted on the caudo-ventral angle of the mesial 

 wall of the pouch; its action is to draw the lower edge of the pouch 

 mesiad beneath the chin. The opening of the cheek pouch, lying 

 just laterad of the mouth opening, is surrounded by a sphincter 

 muscle, which serves to close the mouth of the pouch. See Merriam 

 (1895, pp. 17-19) and Stephens (1906, pp. 141, 142) for further 

 descriptions of the structure and use of the cheek pouches of the 

 pocket gopher. 



Thoracic Limh Muscles. — The muscles of the thoracic limb proper 

 will be taken up in the order in which they appear in the dissec- 

 tion. The plan usually followed in this work was to remove each 

 muscle completely after it had been studied. The advantages of 

 this method are as follows: (1) Origins and insertions can be 

 traced more definitely than when the muscle must be saved for 

 further study. (2) A much clearer view of deep muscles is 

 obtained by removal of the superficial layers. (3) In measuring 

 volumes of muscles, which will be discussed later, it was of course 

 necessary to remove them completely. 



The serial numbers preceding the following descriptions indicate 

 the order in which the muscles may best be studied. These num- 

 bers will also be used occasionally in referring to muscles, and 

 later in the grouping of muscles with a common function. 



1. Cutaneus maximus {cut. max., fig. M). — This is the first 

 muscle encountered on removal of the skin, being very difficult to 

 separate from the latter. It forms a thin sheet over the back, 

 flanks and abdomen, arising from the subcutaneus fascia and joining 

 with its fellow of the opposite side in the dorsal and ventral mid- 

 lines. On the sides of the thorax the fibers converge to form a 

 thick band which joins the pectoralis quartus and is inserted with 

 it on the antero-mesial surface of the humerus just below the lesser 



