568 PHOCA VITULINA HARBOR SEAL. 



Without going into a detailed comparison of the bones of the 

 general skeleton, a few points may be briefly noticed. The 

 scapula has nearly the same general outline in both P. vitu- 

 lina and P. fcetida, but differs widely from that of P. grcenlan- 

 dica, mainly through the great development of the posterior 

 upper portion of the blade, which is greatest in P. vitulina. In 

 other words the scapula in P. grcenlandica is less " sickle-shaped" 

 than in the others owing to the greater development of the pre- 

 scapular portion and the less development of the post-scapular 

 part. In P. fcetida the infra-acrornial portion is much elongated, 

 so that although the scapula is much smaller than in P. vitulina, 

 its length is greater. In P. fcetida the length to the breadth* 

 is as 1 to 0.847 ; in P. vitulina, as 1 to 1.155 ; in P. grcenlandica 

 as 1 to 0.908. The width of the post-scapular fossa to the whole 

 breadth is, in P.fcetida, as 0.577 to 1 ; in P. vitulina as 0.609 to 

 1 ; in P. grcenlandica as O.CG4 to 1. 



The bones of both the fore and the hind limbs vary considera- 

 bly in size and form with each species, but only the difference 

 in the relative length of the several segments of the limb, com 

 pared with its whole length, will be here noted. In both fore 

 and hind limbs the second segment is relatively much shorter 

 in P. vitulina than in either P. fcetida or P. grcenlandica ; in P. 

 grcenlandica the pes is relatively much lengthened while the 

 manus is of the same length as in P. vitulina. The proportion- 

 ate length of the femur to the tibia varies as follows : in P.fce- 

 tida the femur to the tibia is as 1 to 2; in P. vitulina as 1 to 1.8; 

 in P. grcenlandica as 1 to 2.3. The proportionate length of the 

 femur to the pes is as 1 to 2.7 in P.fcetida, 1 to 2.4 in P. vitulina, 

 and 1 to 2.9 in P. grosnlandica ; of the femur to the whole limb, 

 respectively, 1 to 5.7 ; 1 to 4.3 ; 1 to 6.2. This difference is mainly 

 due to two elements of variation, the shortness of the tibia in 

 P. vitulina and the great length of the pes in P. grcenlandica. 

 The ratio of the pes to the whole limb, however, is nearly con- 

 stant, being as follows : in P. fcetida, 1 to 2.14 ; in P. vitulina, 1 

 to 2.16 ; in P. grcenlandica, 1 to 2.13. 



P. vitulina presents another noteworthy point of difference 

 from its allies in the relative shortness of the pelvic bones, which 

 is directly proportionate to that of the tibia and radius, or second 

 limb segments. In both P. vitulina and P. grcenlandica the length 



* The supra-scapular epiphysis is iu each case omitted from the compari- 

 son, and only the scapulae of adults of comparable ages are employed. 



