THE PELVIC LIMB 



It will be noted (fig. 52) that the sea-lion has a lesser trochanter de- 

 fining insertion of the psoas magnus and iliacus (so-called), while in 

 the seal these muscles have fascial insertion over the knee and there is 

 no lesser trochanter. In this illustration it may also be noted that 

 while in the sea-lion the inner condyle of the femur extends but a 

 trifle more distad than the outer, in the seal this discrepancy is very 

 marked indeed. The result of this is that when the femur is held at a 

 right angle to the body axis the position of the condyles will cause 

 greater supination of the pes, so that the soles may be maintained paral- 

 lel with greater ease. If the femur be extended beyond a right angle, 

 then the condylar conformation will cause the feet to be held more ele- 

 vated. 



A peculiarity which affects function in the pinniped knee is the length 

 of the tibial collateral ligament. The distal attachment of this is not 

 at approximately one-tenth the distance from the knee to the ankle, 

 as in the cat, but at a point about one-quarter or two-fifths this distance. 

 This allows for considerable rotation through the knee, with the fibular 

 ligament as the pivot. In most other mammals such rotaton of the 

 shank can be accomplished through the hip joint, but because of the po- 

 sition of the short femur in the Pinnipedia such action is impossible in 

 this order without adductive-abductive movements of the thigh. 



A further accompaniment of the above conditions of the femur and its 

 more intimate musculature is that the function of those muscles which 

 normally act as extensors of the thigh through an attachment in the vi- 

 cinity of the knee joint are enabled to alter their function. Their inser- 

 tions have either migrated wholly or in part distad, and accordingly 

 they now operate to bind down the shank and accomplish its adduction 

 or elevation, according to posture. There is considerable variation in the 

 form of these muscles as between the seal and the sea-lion (figs. 22 

 and 23), but in both animals the gracilis, semitendinosus and semimem- 

 branosus act especially in this capacity and their insertions not only do 

 not approach the knee but are extended onto the heel by fascia in the 

 case of the sea-lion, and in the seal by a more tendinous structure pass- 

 ing to the plantar fascia. In the former animal the biceps acts with par- 

 ticular efficacy as a binder, but not to the same extent in the seal. The 

 conformation of these muscles has naturally affected the position of the 

 crotch, or posterior integumental border between the leg and body, or in 

 this case the tail, so that in both animals this lies approximately at the 

 heel and all of the hind limb except the pes is contained within the body 

 contour. 



[295] 



