36 PROCEEDINGS OF THE NATIONAL MUSEUM vol.73 



'laterad of the ilium in the Phoca has been caused chiefly by the 

 iliocostalis portion of the back musculature, attached to almost the 

 whole anterior (or " medial ") face of the bone. As the femur is 

 very short in this order, there is no need for a long ilium or long 

 leverage for the flexors of the thigh. In both animals the inser- 

 tions of the muscles extending from the posterior innominate to the 

 knee and shank have migrated distad, and in order to increase the 

 lever arm, there has also been a lengthening of the ischium and pubis. 

 AVliy this should be marked in Zalophus is not so clear, for the 

 muscles concerned are not of such fundamental importance to that 

 animal ; but this increased leverage — so well developed in the Phoca — 

 is of basic importance in the adductional movements employed in 

 swimming. In this animal there has also been some extension 

 dorsad of the spine from which arises a part of the biceps femoris, 

 which allows an elevation of the flippers in characteristic fashion, 

 and ventrad of the inferior tuberosity of the ischium, adding to the 

 effective range of movement. 



The remainder of the muscular stimuli which operate upon the 

 innominate are so complex and so involved with phylogeny and 

 angles of leverage that a discussion in further detail is hardly justi- 

 fied. There may, however, be mentioned the greater prominence in 

 Zalophus of the rectus femoris process, cranio-ventrad of the ace- 

 tabulum, hardly more than a rugosity in Phoca. There is a single 

 psoas-pectineal process in Zalophus^ represented in Phoca by a 

 large psoas magnus process, more cranially and ventrally placed, 

 and a faint psoas minor process more caudad, while the pectineus 

 arises from no prominence at all but has fleshy origin from the 

 border of the pubis. There is no fused symphysis pubis in either 

 animal, but this term is employed for convenience to designate this 

 region; and there is an ischial epiphysis in both, located caudad and 

 probably the more extensive in Phoca, but this is difficult to deter- 

 mine in the skeletons available. 



Posterior limb. — The length of leg from a functional standpoint 

 is of a questionable degree of value for the reasons not only that all 

 but the pes is within the body covering, but also because the normal 

 and more or less fixed position of the femur is flexed in the Zalophus 

 and somewhat extended in the Phoca. The length of the hind limb 

 is considered as constituting the sum of the lengths of the femur 

 (head to condyle), tibia, and the distance from the tip of the second 

 toe (exclusive of the nail in Phoca) to the posterior part of the 

 astragalinar condyle. In Zalophus this is 62, and in the Phoca, 74 

 per cent of the body length (104 in a cat). 



Thigh: Femur. — In the Zalophus the femur is 18 and in the 

 Phoca 16 per cent of the limb (33 in a cat) ; of the tibia, 50 and 40 

 per cent; and in relation to the body length 11 and 12 per cent, re- 



