i 



AUT. 15 ANATOMY OP THE EAEED AND EARLESS SEALS HOWELL 119 



In Zalophus the manus continues from the antibrachium in almost 

 a straight line, in static position the axis divergine; from this by not 

 more than 15°, with adduction almost zero and abduction to 45° (in 

 the partially dissected specimen). In the Phoca the static position 

 of the manus is at an abducted angle with the forearm of about 45°. 

 Adduction from this position is almost entirely inhibited by the ten- 

 sion of the abductor digiti quinti — probably slightly more yielding in 

 life — but maximum abduction is to an angle of 90° with the forearm. 

 As already mentioned the proximal articular surfaces of the Zalophus 

 scapholunar and ulnare, and of the metacarpals extend farther upon 

 the dorsum of these bones than in the Plioca^ but it was found that in 

 the preserved animal the chief center of movement was at the articu- 

 lations distad of the scapholunar and ulnare, due to the looseness of 

 the capsular tissue at this point. Extension of the manus allows the 

 metacarpals to be placed at a right angle to the forearm but no more, 

 while almost the same amount of flexion is permitted. Provision is 

 not made at the articular surfaces of the carpal bones of the Phoca 

 for the same amount of extension, but this is nevertheless permitted 

 by the looseness of connection of all the carpal bones. This same 

 looseness allows flexion to the excessive point where the metacarpals 

 are parallel with the bones of the forearm (after removal of the 

 integument and fatty tissue). As there has been no twisting of the 

 antibrachial bones the manus, in relaxed posture, presents its radial 

 border almost directly craniad. Presumably'' this position is the best 

 in both animals for the work which the manus has to perform, as it 

 certainly is for terrestrial locomotion in Zalophus, disposing of the 

 Jong tip of , the manus in a way that will interfere the least with 

 walking. 



There seems to be little of functional significance in the carpus of 

 Zalophus, as it is just the sort one would expect to find between the 

 broad antibrachium and the metacarpus. There are several points 

 about the carpus of Phoca, however, which attract attention. It is 

 rather narrow proximad, which has probably been brought about by 

 much movement of the manus in the plane of abduction-adduction. 

 Abduction is very materially assisted by the peculiar abductor digiti 

 quinti. As this has become more specialized it has pulled the manus 

 more and more laterad until now its natural tone prevents adduction 

 of this segment even as far as the antibrachial axis. Abduction to 

 90° is possible, however, as already mentioned, and this is correlated 

 with a specialized, " mitred " condition of the carpus as a whole, sug- 

 gestive of the mitering at the corner of a picture frame. The carpus 

 alone has responded to this stimulus — not the distal extremity of the 

 antibrachium. In brief this consists of a slight rearrangement of 

 the carpal elements so that the metacarpal base of the first digit has 



