REPORT ON THE SEALS. 49 



of the bone immediately below the condylar surface. The shaft of the tibia was 

 divided into three surfaces in its upper part, but in the lower half the ventral and outer 

 surfaces were not so sharply differentiated from each other. The lower end of the 

 inner and posterior surfaces of the tibia had two longitudinal grooves, the inner for the 

 tibialis posticus being both wider and deeper than the outer for the flexor longus 

 liallucis. On its inner side a short malleolus projected downwards. The tibia articu- 

 lated below with the fibula and the upper surface of the astragalus. The tibia differed 

 from that of Leptonychotes in having a much less transverse diameter at the condylar 

 end, in not possessing a definite ridge on the shaft for the gracilis, in not being so 

 distinctly grooved at the lower end in front for the tibialis anticus, and in being more 

 deeply grooved behind for the tibialis posticus and flexor longus hallucis. 



The fibula was a slender bone, 213 mm. long. Its upper end was fused with the 

 outer tuberosity of the tibia. The shaft was three-sided all the way down. A short 

 malleolus projected from the lower end which articulated by movable joints both with 

 the tibia and the external lateral surface of the astragalus, and was grooved externally 

 for the peronei ; it did not articulate with the os calcis, and the malleolus generally was 

 much less bulky than in Leptonychotes. In Arctocephalus gazclla the tibia was 180 

 mm. and the fibula 163 mm. long, and the epiphyses were not ankylosed. 



Pes. — The tarsus contained eight bones. The astragalus possessed a trochlear 

 surface superiorly, which articulated with the lower end of the tibia ; internally it did 

 not articulate with the tibia, and externally it had a broad surface for the external 

 malleolus of the fibula, which looked forwards as well as outwards, but was not however 

 relatively so large as in Macrorhinus and Leptonychotes; anteriorly it had a convex 

 head for the scaphoid, immediately external to which was a narrow articular surface 

 for the cuboid ; inferiorly its articular surface was divided into two parts, separated 

 by an interosseous ligament, for the os calcis ; the posterior surface was narrow and 

 grooved, and not prolonged into a calcanear process. The extreme length of the 

 astragalus was 40 mm. 



The os calcis was elongated behind into a strong calcanear process, which was 

 grooved posteriorly for the tendon of the plantaris. Its outer surface was also marked 

 by the peronei tendons, the position of which was expressed by a strong tubercle and 

 by two grooves ; superiorly it articulated with the astragalus, and anteriorly with the 

 cuboid. The extreme length of the os calcis was 54 mm. 



The cuboid had both a plantar ridge and a peroneal groove. It articulated behind 

 with the os calcis, internally with the scaphoid and external cuneiform, anteriorly with 

 the 4th and 5 th metatarsals. 



The scaphoid had the usual shape of the bone, but without a tubercle ; it articu- 

 lated behind with the astragalus, externally with the cuboid, internally with the ento- 

 scaphoid bone, anteriorly by three very distinct facets with the cuneiforms. 



(zool. chall. exp. — part Lxvin. — 1888.) Yyy 7 



