AQUATIC MAMMALS 



ing how much similarity may exist between actual phalanges and a pre- 

 digital item. This is of much interest and will be discussed later. 



The manus of the seal and sea-lion could not be more utterly unlike 

 were they totally unrelated, and they must be discussed from a different 

 angle. 



In the normal posture assumed by the seal the manus is the only part 

 of the arm that projects beyond the body contour, the external axilla 

 of the specimen dissected falling opposite the pisiform bone. The 

 manus is not appreciably altered in relation to body length from the 

 condition obtaining in such a terrestrial carnivore as the cat, but as so 

 much of the arm is out of sight the hand appears unduly short. It 

 is very broad, however, this being largely due to fatty tissue, skin, and 

 hair. The digits are all completely connected by membranes, but these 

 are narrow and do not permit spreading of the digits so as to present 

 a broad surface to the water. In Phoca the first digit is the longest 

 and heaviest, the others being successively slightly shorter, and all are 

 furnished with heavy nails. And this is the case in most seals, although 

 perhaps in none are the nails relatively heavier than in P. hispida, 

 while a few have them slightly lighter, and Beddard (1900) has 

 stated that in Ommatophoca they are quite rudimentary. In mounted 

 Mirounga examined they are short and blunt as though worn down 

 by much use. The conformation of the arm would permit of the nails 

 being used for scratching over but a negligible area of hide, so they 

 must have some other function, else they would almost certainly have 

 become atrophied. This may consist either of scratching holes in the 

 ice or prying about on the ocean floor. 



As there has been no rotation of the long bones of the pinniped arm 

 the radial border of the manus is presented directly forward, and it can 

 accordingly be pressed flat against the body without either pronation or 

 supination from the normal. While dissecting Phoca it was found that 

 the static posture of this segment is markedly abducted with respect to 

 the antibrachial axis, this being through an arc of more than 45 de- 

 grees. From this position adduction cannot be great, the chief in- 

 hibitor being the peculiar abductor digiti quinti longus, but the latter 

 helps in further abduction, which is possible to an angle with the anti- 

 brachial axis of at least 90 degrees. Provision is apparently not made 

 upon the articular surfaces of the phocid scapholunar and ulnare for 

 extension of the manus to 90 degrees, but nevertheless such extension 

 seems possible because of the looseness of the ligamentous connections. 

 Of course these may not have been so loose in life, but it is likely that 



[248} 



