AST. 15 AKATOMY OF THE EARED AND EARLESS SEALS HOWELL 41 



drical, while in the latter it tapers from both ends toward the center, 

 and there are two well defined fossae — one cranio-laterad, from 

 which arises the peroneus brevis, and the other caudad, giving origin 

 to the flexor hallucis longus. In the otariid the origins of both these 

 muscles have a somewhat different relationship in regard to the fibula. 

 The distal head of the otariid fibula is rather short, being definitely 

 shorter than is the medial malleolus, relatively smooth and without 

 grooves, and with but slight articulation with the ankle. In the 

 Phoca the fibula projects distad of the medial malleolus, its surface 

 for articulation with the ankle is almost as extensive as that of the 

 tibia, and there are two very deep grooves laterad. The more caudal 

 of these is for the peroneus digiti quinti, and the more cranial for 

 the peroneus longus. 



Foot. — If the osteological length of the foot for the present purpose 

 be considered as comprising the distance from the tip of the terminal 

 phalanx of the second digit to the caudal part of the condyle of the 

 astragalus, then for the Zalophus and the Phoca., respectively, it con- 

 stitutes 28 and 34 per cent of the body length, and 45 per cent of the 

 leg length in both. 



The tarsal elements of these two pinnipeds comprise astragalus, 

 calcaneum, centrale, first, second, and third tarsales, cuboid, and a 

 medial sesamoid. The astragalus is especially interesting and ex- 

 hibits differences of much significance. In the Zaloyhus the position 

 of this bone is slightly more dorsad of the calcaneum, the tibial facet 

 is much larger than the fibular and its slope is more sharply ventrad, 

 in part to compensate for the more distal position in this animal of 

 the medial malleolus as compared to the lateral. This facet extends 

 craniad in Zalophus only just onto the neck, and caudad in the Phoca 

 only onto the posterior extension of the bone. From the fibular 

 facet there is a broad process extending cranio-laterad, absent in the 

 Phoca., and in the Zalophus, a constricted neck and expanded head, 

 with an extensive, rounded facet for articulation with the centrale. 

 In the Phoca the neck is of greater diameter than the head, and 

 ventrad the articular facet is more extensive, a result of the greater 

 degree of movement possible in this animal. In the Zalophus no 

 part of the bone extends caudad of the tibial facet for a greater 

 distance than a couple of millimeters. In the Phoca the astragalus 

 is prolonged caudad in a truly remarkable process which extends 

 beyond the termination of the calcaneum and is grooved for the pas- 

 sage of the flexor hallucis longus tendon. It is the tendon of this 

 muscle only and its tension operating on the process of the astragalus, 

 tliat prevents the foot of Phoca from assuming a position at a right 

 angle to the shank. 



The calcaneum of Zalophus is markedly constricted in the middle, 

 being moderately expanded caudad and greatly so craniad, but that 



