AET. 15 ANATOMY OF THE EARED AND EARLESS SEALS HOWELL 95 



latter and vice versa. In the former the more medial arose directly 

 superficial to the lateral. My nomenclature is based on the fact that 

 in the Phoca the muscle which I term the digitorum longus was 

 located in its normal position mediae! to the hallucis, and in both my 

 animals, the digitorum tendon is the one located nearer the calca- 

 neum than the hallucis where they both pass over the heel. It is 

 fully realized that the positions of the tendons at this point could 

 be transposed, but it is necessary to have some criterion and as both 

 muscles are served by the tibial nerve, homologizing by the innerva- 

 tion in such specialized mammals would not be dependable. 



M. Hexor digitorum longus (figs. 13, 27, 28) in the Zalophtis arose deep 

 to the poj^liteus and superficial to the flexor hallucis longus. Its 

 ctrigin was from the caudo-medial part of the head of the fibula and 

 from the strong tibio-fibular ligament which stretched from the 

 head of the latter bone to a point distad three-quarters the length of 

 the tibial shaft, which ligament marked the medial border of the 

 deep fascia of the shank. The tendon from this muscle passed over 

 the more lateral of the two grooves upon the medial border of the 

 caudal tibia, expanded and joined the tendon of the hallucis longus 

 upon its deep surface. The two layers could be dissected apart, 

 however, when it was seen that the digitorum longus sheet split into 

 three branches, these going, respectively, to digits 1, 3, and 4. In 

 the Phoca this muscle was considerably smaller than the flexor 

 Iiallucis but was still a robust muscle. Origin was fleshy from the 

 tibial side of the head of the fibula and from the adjoining border of 

 the posterior tibial fossa as far as the internal lateral ligament. The 

 tendon passed caudad of the internal malleolus and broadened as it 

 extended deep to, and became fused with, the hallucis longus. After 

 careful dissection it appeared that branches of this tendon extended 

 to digits 2, 3, and 4. 



This is Murie's flexor longus halluci^ — a fact not mentioned by 

 Miller — and its origin was simlar to Zalophus^ but the precise inser- 

 tion is not clear. Miller considered it in the same light as I do for 

 PJioca at least, but I can judge little regarding his description of 

 conditions in Arctocephalus. 



M. Hexor hallucis longus (figs. 13, 26, 27, 28) is a somewhat ambiguous 

 name as far as concerns Zaiophus, but for this genus flexor fibularis 

 would be no better. In the Zaiophus it arose deep to the flexor digi- 

 torum longus from the caudal part of the tibial border of the fibula 

 and from the interosseous membrane, but at no point did fibei-s 

 quite reach the tibia. The tendon then passed over the heel between 

 those of the plantaris and digitorum longus, expanded, and formed 

 the more superficial layer of the sheet common to this muscle and the 

 digitorum longus. Further dissection showed that it split into but 

 two branches, which extended respectively to digits 2 and 5. The 



