1916] HolUger: Anatomical Adaptations in the Pocket Gopher 449 



would undoubtedly be profitable in connection with this investiga- 

 tion. But since so complete an anatomical study was impracticable, 

 it was necessary to select the structures employed in some particular 

 function for close examination. The structures selected are those 

 which most markedly distinguish the gopher from other rodents, 

 namely, those associated with its fossorial, or underground, habit of 

 life. The parts affected to the greatest extent by this mode of life 

 are those connected with digging in the ground — namely, the bones 

 and muscles of the anterior limb. A correlation of the fossorial 

 habits of the gopher with the specialization in the anatomy of the 

 thoracic limb is therefore the particular subject of the present 

 study. 



As material for comparison with the gopher, numerous rodents 

 were available. The California ground squirrel (Citellus heecheyi) 

 was selected because it belongs to one of the most primitive rodent 

 groups living at the present time. The brown rat (Epimys nor- 

 vegicus) was chosen because it is also a primitive form, and one 

 little known anatomically, though the animal is so common. As a 

 typical cursorial or surface-dwelling type of rodent, the Sacramento 

 Valley cottontail {Sylvilagus auduboni) was first used. Later some 

 specimens of the California jack rabbit (Lepus calif ornicus) , which - 

 is undoubtedly one of the most specialized of the rabbits, were 

 secured. The Belgian hare (Lepus europaeus) was also employed in 

 the earlier stages of the work. The anatomy of the hare is of 

 interest chiefly in showing the effects of domestication on a special- 

 ized form. The Sierra chickaree or red squirrel (Sciurus douglasi 

 alholimhatus) was taken as the type of arboreal or tree-dwelling 

 rodent. The list of material studied thus includes rodents which 

 have become adapted to the three principal modes of mammalian 

 life, namely, fossorial, cursorial, and arboreal. 



Habits of the Rodents Studied 



The gopher passes practically its entire life underground. It 

 seldom comes to the surface, and still more rarely quits its burrow 

 entirely. It digs long tunnels several inches below the surface of 

 the ground, occasionally making an opening for the purpose of 

 pushing out the dirt. Actual digging is accomplished by means 

 of powerful downward and backward strokes of the front feet. 

 The strokes are made alternately with the right and the left foot, 



