1916] HolUger: Anatomical Adaptations in the Pocket Gopher 451 



and also figures to show the origins and insertions of the muscles 

 after these had been verified. 



The next step was to compare the bones and muscles of the 

 gopher with homologous structures in the other forms. In order to 

 make these comparisons as definite as possible the quantitative 

 method, explained later, was adopted. With the figures provided 

 by these measurements it was then possible to draw certain con- 

 clusions bearing upon the principal subject under investigation, 

 namely, the correlation or lack of correlation between anatomical 

 specialization and habits of life. 



Osteology 



The bones of the gopher with which this study is chiefiy con- 

 cerned are those forming the shoulder girdle, and the skeleton of 

 the thoracic limb. While some of the muscles which furnish motive 

 power to the limb originate on the skull, on the vertebrae, on the 

 sternum, and on the ribs, as described in the discussion of muscles, 

 it is outside our province to study in detail all of the above-named 

 bony structures. Moreover, the bones of the foreleg exhibit most 

 strongly the modifications correlated with the fossorial habits of the 

 gopher. 



The most noticeable general characteristic of the bones of the 

 anterior leg of the gopher is their irregularity of outline. The 

 various processes for muscular attachment, such as the spine of the 

 scapula, the deltoid tuberosity and the condyles of the humerus, 

 the olecranon of the ulna, and the pisiform bone of the carpus, are 

 very noticeably larger in the gopher than in any of the other rodent 

 forms dissected. If, as is probably true, we may infer the strength 

 of a given muscle, or set of muscles, from the size of the bony 

 tuberosity to which it is attached, we may say at once that the 

 gopher has more powerful muscles in proportion to its size than any 

 of the other species of rodents studied. Next to the gopher in 

 irregularity of bones is the brown rat and then the ground squirrel. 

 Thus the digging rodents have the most irregularly shaped bones, 

 and by inference the most powerful muscles. The bones of the 

 rabbits are the smoothest. If the relative length of the olecranon 

 process in the different forms be taken as an index of the irregu- 

 larity of the bones in general, we find (see table 2, p. 487) that 

 the gopher stands at the head, and the jack rabbit at the bottom of 

 the list of rodents studied. 



