42 PROFESSOR STRUTHERS. 



Keading down the columns, comparing the breadth with the 

 thickness of each bone, the flattening goes on progressively, in 

 B. musculus, in all, becoming more and more marked. It is 

 but little on the metacarpal bone of digit III., and on digit II. 

 after the metacarpal. In my 65 to 6G-feet-long B. mvisculus, as 

 in Megaptera, the thickness of the 2nd bone of digit II. is 

 greater than the breadth, the shaft being excavated to make 

 room for the first node of digit III., but no other bone in 

 digit II. of that B. musculus is thicker than it is broad. In 

 Megaptera, the 2nd bone of digit II. is thicker than broad, owing 

 to the adaptation above mentioned, and these two measure- 

 ments are equal in the 2nd bone of digit III., and in the 3rd 

 bone of digit IV. The metacarpals of digits III. and IV. in 

 B. musculus are a little thicker in proportion to their breadth 

 than the first phalanx is, which is not the case in Megaptera. 

 Comparing digits III. and IV. of Megaptera, the first two bones 

 of digit III. are thicker in proportion to their breadth than 

 those of digit IV., but this proportion is reversed on the 3rd, 

 4th, 5th, and 6th bones of these two digits. Hence the more 

 slender appearance of the bones of digit IV. in proportion to 

 their length, viewed along the surface. 



Viewing the digital bones of Megaptera, these measurements 

 show that there is a variable proportion between the robustness 

 and the length. In digit II. the metacarpal has the same length 

 as that of digit IV. but it is twice as robust. Its 2nd bone also, 

 and to some extent its 3rd, are more robust, in proportion to 

 their length, than the corresponding bones of digit IV. All 

 along digits III. and IV., the greater robustness of the bones 

 of the former, in proportion to their length, is striking. In 

 digit III. the third bone is actually more robust than the 2nd, 

 and it is If inch shorter. Its remaining phalanges also are 

 more robust than the 2nd bone, in proportion to their length. 

 This is after digit III. has ceased to be splinted on its radial 

 side by digit II. In like manner in digit IV., the 2nd bone is 

 not so robust, in proportion to its length, as the bones beyond 

 it, but this is not to so marked an extent on the immediately 

 succeeding bone as in digit III. In digit V., however, the 3rd 

 and 4th bones are not more robust in proportion to their length 

 than the 2nd bone. 



