AQUATIC MAMMALS 



fourth digits, while in the others this is compHcated by a flexional ten- 

 dency progressively in a radial direction, so that the pollex is almost as 

 much flexed as abducted. It is difficult to express this in words but 

 the illustration (fig. 35) shows it quite clearly. In reality there has 

 been partial rotation of the first digits and an increasingly lesser amount 

 in the others, so that extension of the thumb really helps to adduct it 

 (in relation to the antibrachial axis) . 



With the exception of the radial grooves or pulleys, as already noted, 

 the extensor muscles of the phocid manus show nothing that may be 

 deemed of much significance. The flexor muscles, however, exhibit 

 several points of interest. The tendon of the palmaris longus broadens 

 so as to cover the whole radial half, including the border, of the palm. 

 The flexor carpi ulnaris tendon does the same to cover the entire palm. 

 The peculiar abductor digiti quinti longus has already been mentioned. 

 The origin of these three muscles from the broadened olecranol part of 

 the ulna, in connection with the normally abducted posture of the 

 manus, makes it likely that all three of them have more the function of 

 effecting still more marked abduction of this member, than of flexors. 

 Apparently the chief muscle for the accomplishment of flexion is the 

 flexor communis, as indicated by the excessive breadth of its origin and 

 of its common tendon, and it acts chiefly as a flexor of the manus as a 

 whole, rather than of individual digits. 



In recapitulation it may be said that the anatomical characters of the 

 phocid manus, and what they indicate, is precisely in conformity with 

 what one would expect did one bind down his own arm in phocid pos- 

 ture and attempt to move the manus similarly. Almost all mobility 

 would be through the carpus, which would have to be adapted for an 

 extreme amount of abduction and extension. Such mobility is useful 

 in fiddling movements of the manus in making slight adjustments of 

 posture while floating, just as in the case of a human swimmer, but in 

 order to explain the degree of alteration which we find in this member 

 of Phoca it is necessary to assume that it has some other important ac- 

 tion, involving a considerable degree of strength, than any which is 

 now surely known. 



As in the seal the radial border of the manus of the sea-lion is pre- 

 sented directly forward so that it offers the least possible resistance to 

 the water. The external part of the limb has the shape of a long, rather 

 falcate paddle, thicker upon the anterior border and thinner upon the 

 hinder edge. The external axillary angle is about at the middle of the 

 fore arm, so that the distal half of this segment in reality constitutes 



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