462 University of California Publications in Zoology [Vol. 13 



in the middle finger the skeleton of the claw is as long as the two 

 proximal phalanges together. In life these terminal phalanges are 

 covered by the sharp, horny claws, which increase their length con- 

 siderably. Sesamoid bones are found on the palmar surface of the 

 distal phalangeal joints. 



The phalanges of the rabbits are short and slender and the 

 claws are blunt. The squirrels have well developed phalanges 

 except in the first digit, which is only about one-sixth as long as 

 the third. The claws of the chickaree are long, curved, and sharp. 

 The manus of the rat is relatively smaller than that of the gopher, 

 and the claws are much shorter; digit 1 is shorter and digit 5 

 longer than corresponding members in the gopher. 



Myology 



The arrangement of the muscles of the anterior limb of the 

 gopher resembles to a considerable extent that found in the rabbit, 

 though several important differences will be noted in their proper 

 places. In certain respects the musculature of the gopher is more 

 like that of the ground squirrel or rat than like that of the rabbit, 

 but since the latter animal is the rodent type most frequently used 

 in laboratory study, our comparisons will usually be based on the 

 muscular structure of the rabbit. At the same time, instances of 

 close resemblance to other of the forms studied in this connection 

 will be noted. 



Cheek-Pouch Muscles. — The cheek pouches of the gopher are at 

 least as highly developed as those of any other rodent, and while 

 the musculature of these pouches has no connection with that of 

 the anterior limb, it is interesting enough to merit a few words of 

 description. Figure M shows the arrangement of these structures. 

 The cheek pouches are sacs of skin lined with soft, short hairs; 

 they extend from the angles of the mouth back to the shoulder 

 where they cover the deltoid muscles. They are suspended along 

 the sides of the cheek by fascia and muscle fibers, the latter having 

 been described under the following names (Merriam, 1895, p. 101) : 

 The protractor of the pouch comprises fibers arising from the fascia 

 of the masseter muscle ; these fibers pass ventrad and caudad and 

 spread out over the mesial and lateral surfaces of the pouch. 

 Their contraction draws the posterior end of the pouch forward 

 and assists in emptying it. The levator of the pouch arises along 

 the caudal half of the nuchal ligament and passes laterad and 



