40 PROFESSOR STRUTHERS. 



The measurements of these bones were all made along the 

 middle to avoid fallacy arising from these variously shaped 

 ends. In the Megaptera there is very little of the cupping at 

 the ends, though it is discernible at the first nodes of digits II., 

 III., and IV. But the oblique cutting of the ends in digits II. 

 and V., giving the wedge-shaped node, is distinct, and the same 

 is seen on digits III. and IV. after they have passed beyond the 

 lateral digits, the base of the wedge towards the free border of 

 each. This wedge form of the node must tend to give the 

 digits more lateral movement from the axis of the limb, as in 

 spreading the fingers. 



In all the specimens of B. musculus the finger bones have 

 the hour-glass form. The expansion at the ends is less on the 

 metacarpals, owing to the greater breadth of the shafts, and is 

 least at the carpal end of the two middle digits. The hour- 

 glass form is less marked on the three distal phalanges of the 

 long fingers and on the two distal of the shorter fingers, as 

 the phalanges become more flattened. Roughly speaking, the 

 expanded ends are about twice the breadth of the shaft, at the 

 middle. The above applies to Megaptera also with the follow- 

 ing peculiarities. In digit II. the metacarpal presents less 

 expansion owing to the great robustness of its shaft, but its 

 other two bones have the most hour-glass form of all the finger 

 bones. The excavation of their shaft accommodates the first 

 and second nodes of digit III., but is no less marked on their 

 free border, owing to the great expansion at their ends to sup- 

 port the large nodes whicli project on their free border. The 

 excavation on the ulnar side of the first phalanx of digit II. to 

 receive the first node of digit III., flattens the border so much 

 as to give the shaft a prismatic form. A like excavation and 

 flattening is seen on the much smaller corresponding bone in 

 B. musculus. The bones of digit IV. appear slender in the 

 series in Megaptera compared with B. musculus, owing not only 

 to the great robustness of digit III. but likewise to that of 

 digit II. But comparing simply the two long digits in Megap- 

 tera and in B. musculus, the relative slenderness of digit IV. in 

 Megaptera is striking, 



Breadth and Thickness of the Digital Bones. The measure- 

 ments given in Table IV., showing the breadth and thickness of 



