470 University of California Publications in Zoology [Vol. 13 



laris. Its action on the shoulder girdle is similar to that of the 

 preceding three muscles. 



11. Pectoralis {pec, figs. 0, P, R) is extremely well developed 

 in the gopher; as in the rabbit, it consists of four parts. 



a. Pectoralis primus arises from the manubrium of the sternum 

 and is inserted on the mesial surface of the distal part of the del- 

 toid tuberosity of the humerus. 



&. Pectoralis secundus arises along the lateral part of the 

 sternum from the manubrium to the xiphoid cartilage ; it is inserted 

 on the humerus with 11a (pec. sec, pi. 39). 



c. Pectoralis tertius arises from the sternum and costal cartil- 

 ages from the second to the fifth, inclusive. It is entirely covered 

 by 11a and 11&, and the fibers pass more cephalad to be inserted on 

 the mesial surface of the coracoid process of the scapula {pec ter., 

 pi. 89). 



d. Pectoralis quartus arises from the xiphoid cartilage of the 

 sternum and the abdominal fascia ; it passes forward and outward 

 to be inserted in common with the cutaneus maximus on the mesial 

 surface of the proximal part of the deltoid tuberosity {pec quar., 

 pi. 39). It will be noted (fig. 0) that these fibers pass beneath 

 those of 11a and 11&, an arrangement resembling that found in the 

 human pectoralis major. 



The pectoralis of the gopher is an important muscle in digging. 

 Its insertion is well down on the humerus, increasing the leverage of 

 this muscle and rendering the downward and backward stroke of 

 the arm more powerful. 



12. Suhclavius (5w6cL, fig. R) is a small and unimportant muscle 

 arising from the junction of the first rib with its costal cartilage, 

 and inserted on the dorsal and caudal surfaces of the lateral half of 

 the clavicle. It helps to hold the clavicle in place. 



13. Serratus anterior {ser. ant., fig. P). As in all quadrupeds, 

 this muscle is important in suspending the body between the fore 

 legs; the two serrati form a sling in which the thorax rests. In 

 contracting they pull the scapula downward or the body upward, 

 depending upon which is the fixed point. There are two parts to 

 this muscle, between which the largest part of the scalenus passes 

 {seal., fig. 0). 



a. The cervical portion arises from the transverse processes of 

 cervical vertebrae from the third to the seventh, inclusive, and 

 from the first two ribs ; it is inserted into the cephalic five-sixths 



