THE PECTORAL LIMB 



they were almost so. This same character allows of flexion of the manus 

 after the integument and tissue has been removed to the excessive point 

 where the metacarpals are actually parallel to the fore arm ; so the flexion- 

 extension arc is through 270 degrees. This would hardly be possible 

 in life because of the confining influence of the surface tissue. 



With all of the arm except the hand within the body contour and with 

 the segments somewhat flexed at that, a relaxed position of the manus 

 of the normal sort (i. e. on a line with the fore arm) would bring the 

 palm almost against the body. In this position the body would accord- 

 ingly prevent much flexion of this member (although if the arm be 

 extended or rotated this would not be so and extreme flexion would 

 then be possible), and in order that the manus might be thrust hori- 

 zontally it would have to be extended to almost 90 degrees. Further- 

 more, such extension would seem usually to be initiated from a normally 

 abducted position of the manus (in respect to the antibrachium) . That 

 this is not only so, but that such motions are strong and oft repeated, 

 is indicated by the depth and somewhat lateral inclination of the extensor 

 grooves upon the radial surface in this mammal, as already discussed. 



The change in posture of the phocid manus has brought about some 

 alteration in the carpus. Its ulnar side is weak and has a mitred ap- 

 pearance, because of the normal abduction of the rest of the manus. 

 Carpale 2 is partly interposed between the scapholunar and carpale 1. 

 Crowding has resulted in, or at least has been accompanied by, the as- 

 sumption of a rather conical shape by the carpales, this being especially 

 pronounced in the third, in which the apex is presented dorsad so that 

 from this aspect it appears as a bony point. The ulnare (cuneiform) 

 is reduced in size and the fifth metacarpal subtends that, rather than 

 the lateral side of the unciform, which has the function purely of a 

 fourth carpale. In consequence the fifth digit really appears to be more 

 opposable than the thumb. The abducted posture of the manus places 

 the pisiform at the side of the fifth metacarpal. 



It is seen (fig. 35) that there is a gradual reduction in size of the 

 metacarpals from the first to the third, while the fourth and fifth are 

 abruptly smaller, and this, in connection with carpal details, places the 

 metacarpal-phalangeal articulations on a line. The first phalanx of the 

 pollex is more than twice as long as the first two phalanges of any of 

 the other digits, and this causes the pollex to be the longest. It appears 

 that the assumption of an abducted posture by the hand is partly effected 

 not by pure adduction at the bases of all the digits, but only part of them. 

 Thus there may be said to be pure abduction only of the fifth and 



[249] 



