1916] Holliger: Anatomical Adaptations in the Pocket Gopher 485 



vessels, nerves, and lymphatics, the volume of which was not deter- 

 mined. 



The figures given are from average measurements of several 

 individuals in all cases except the Belgian hare; only one of these 

 animals was dissected. 



Table 1 



Table Showing Relative Volumes of Muscle Groups in the Seven Forms 

 Dissected. In Percentages, Considering the Whole Volume of the Arm 

 Plus Volume of the Bones and Muscles of the Shoulder, as 100 

 Per Cent. 



Muscle GroTips ^ 



O 



Group 1, shoulder-girdle muscles 20.6 



Group 2, draw humerus downward 



and backward 15.3 



Group 3, extensors of upper arm 5.7 



Group 4, flexors of upper arm 9.6 



Group 5, extensors of forearm 7.9 



Group 6, flexors of forearm 4.0 



Group 7, extensors of hand 3.5 



Group 8, flexors of hand 6.1 



Bones and hand, after removal of 



arm muscles 17.5 



Total volume accounted for 90.2 



Deductions from Volumetric Figures 



It now remains to be seen whether or not the data accumulated 

 indicate any correlation between the habits of the different rodents 

 and the development of the various muscle groups. The relation 

 of habit to volume and shape of bones in the different types has 

 already been discussed (see p. 451). The muscles of group 1 are 

 relatively unimportant in the specialized movements of each mam- 

 mal. As has been noted, the actions of these muscles are very 

 complex, and a simple correlation with habits of life could not be 

 expected. While the volume of these muscles varies from 16 per 

 cent in the rat to 22.9 per cent in the ground squirrel, no explana- 

 tion of this variation is apparent. 



Group 2 is composed of muscles which draw the humerus down- 

 ward, backward and inward. This movement would seem to be 

 about equally useful in climbing trees, in digging, and in running; 



cS 



W 



i-D 



o 



B 



la 



22.9 



16.0 



17.4 



19.1 



21.4 



14.8 



18.5 



37.3 



18.4 



12.9 



13.0 



23.6 



6.7 



5.4 



7.2 



12.1 



7.9 



5.3 



9.6 



6.8 



13.6 



11.5 



14.8 



9.8 



10.5 



9.2 



11.7 



10.7 



10.1 



11.9 



3.5 



2.1 



2.3 



2.6 



3.5 



5.5 



4.2 



2.0 



1.4 



1.6 



2.2 



4.3 



4.9 



3.0 



2.9 



2.9 



3.5 



5.3 



10.7 



9.7 



18.2 



11.3 



16.3 



14.4 



91.5 



91.5 



93.1 



84.7 



92.7 



94.9 



