AKT. 15 ANATOMY OF THE EAEED AND EARLESS SEALS HOWELL 127 



disparity between the positions of the femoral condyles of Phoca is 

 considerably more marked, but in the somewhat more extended posi- 

 tion in which the femur of this animal rests this has the same effect 

 of elevating the ankle but to a more marked degree, caused by the 

 more sloping articular head of the shank. This marked elevation of 

 the phocid pes is very characteristic, and I have seen an animal 

 sleeping for an hour or more with the hind feet elevated in a posi- 

 tion which to any other mammal would surely be the height of 

 discomfort. 



A pinniped peculiarity, or at least one that is not shared by the 

 majority of fissipeds, is found in the knee joint. The medial or tibial 

 collateral ligament is not attached at a point about one-tenth the 

 distance from the knee to the ankle, as in the cat, but at a point 

 in Zalophiis about two-fifths, and in the Phoca about one-quarter, 

 this distance. In connection with a loose capsule of the joint the 

 result is that in the Pinnipedia there is permitted at Iwist 40° of 

 rotation of the shanlc with respect to the femur (in the partially 

 dissected specimens), the fibular collateral ligament being the piv- 

 otal cent«r. This I believe to have been brought about chiefly by 

 the fact that during most of the time the hind feet of both the 

 otariids and phocids are maintained with their axes practically con- 

 tinuous with those of the shanks, and in this position rotational 

 movements of the feet would be transmitted to a considerable extent 

 directly to the knees. In the Zalophus only, such rotation of the 

 shank, in the direction of supination, has the effect of adducting the 

 ankle. Flexion and extension of the pinniped shank is largely 

 inhibited, especially in the otariid, by the muscles which bind it 

 down so closely and by the limits of elasticity of the integument iu 

 which it is inclosed. These movements are possible through an arc 

 apparently of only about 15° in the Phoca and even less in Zalophxi'S. 



The fibular head of the Zalophus is placed more caudad of the 

 shank in respect to the direction of the femoral articulation than is 

 the case with Phoca — almost directly caudad of the lateral tuberosity 

 in the former, and caudo-laterad, at an angle of 45° in the latter. 

 In the phocid the tibia is straight, so that the ankle joint " toes out " 

 to an angle of about 45° to the transverse axis of the proximal 

 articular surface of the shank. In the otariid, however, there is 

 rotation of the fibula so that considered in the same light, the trans- 

 verse axis of the ankle joint is parallel to that of iha knee. This 

 means that were these plantigrade fissipeds, the foot of the Phoca 

 would at rest point straight laterad and of the Zcdophws latero- 

 craniad at about 45°, which in fact it very nearly does. In the 

 Zalophus the fibula ends somewhat proximad of the tibia, and the 

 articular surface of the latter is several times the larger. In Phoca 



