450 University of California Publications in Zoology [Vol. 13 



and are so rapid that a continuous buzzing sound may sometimes 

 be heard when the animal is working in hard ground. Three of 

 the claws are extremely long and heavy, but in the species studied 

 (Thomomys hottae) digits one and five are shorter and have blunt 

 claws. The sides of the fingers are provided with long, stiff 

 •bristles which prevent dirt from passing between them; the hand is 

 thus a broad scoop when the digits are separated. The loose earth 

 is passed backward under the body by the fore feet, and the hind 

 feet push it still farther back. C. H. Merriam (1895, p. 16) states 

 that digging is aided by the long upper incisors, which are used as 

 a pick in loosening hard earth; he also states that in pushing out 

 loose earth at the surface the front feet are placed together under 

 the chin, with the hands held vertically, the animal pushing itself 

 forward with its hind feet until the earth is discharged from the 

 opening of the tunnel. Stephens (1904, p. 142) states that in 

 pushing out the loose earth the toes are "turned outward"; this is 

 in line with our own observations made on a live gopher kept in a 

 large glass jar half filled with earth. 



With regard to the habits of the rodents used for purposes of 

 comparison, only a few words are necessarj^ The ground squirrel 

 lives largely underground and does considerable digging, but it 

 prefers to appropriate and inhabit burrows made by other animals. 

 The brown rat digs only occasionally when necessary to reach food 

 or safety. The rabbits, as stated above, are primarily surface- 

 dwelling forms and do little if any digging. Domesticated rabbits 

 and hares, however, often make burrows in the breeding season. 

 The chickaree is a tree-living form, spending but a small part oi 

 its time on the ground. 



Plan of the Work 



The bones of the thoracic limb of the pocket gopher were first 

 studied in detail, and drawings were made of the whole skeleton of 

 the leg, and of each part separately. The muscles of the thoracic 

 region were then worked out. This was the more difficult because 

 there are a number of modifications and changes from the arrange- 

 ments of muscles found in mammals whose myology has been most 

 studied, and because no description of the muscles of the foreleg 

 of the gopher has been found in the literature. Drawings were 

 then made of the muscles of the shoulder and foreleg of the gopher. 



