AQUATIC MAMMALS 



The deeper and most of the superficial parts were indubitably served by 

 the superior gluteal nerve, but whether or not the caudal border of B 

 may have received twigs from the inferior nerve cannot be stated with 

 any certainty. If so then this part would have gluteus maximus affinity. 



The superficial biceps femoris was highly modified much in the man- 

 ner that it is in the Phocidae (fig. 23). It arose from the tuber ischii 

 and spread fanwise to a fascial insertion over the shank from the knee 

 almost to the instep. The deep biceps was almost an exact counterpart 

 of this muscle in both seal and sea-lion. It was very slender, arising 

 from the deep dorsal fascia alone and perhaps a trifle anterior to the 

 acetabulum, and passed to the vicinity of the outer malleolus of the 

 ankle. 



It is frequently difficult to establish the homology of the semitendi- 

 nosus and semimembranosus for the reason that they often shift about 

 and the innervation is not particularly distinctive. Hence homology 

 can seldom be indubitably established and one must name them as best 

 he can, judging by generalities. In the sea otter the apparent semi- 

 tendinosus is phenomenally developed, to a greater extent than in any 

 mammal known to the writer. Origin is very broadly by fascia, the 

 muscle increases in thickness and most of it passes to the medial side of 

 the leg, where it inserts broadly along the shank, distad to its middle 

 and partly under cover of the gracilis. Oddly enough, however, the 

 fibers along the cranial border do not pass mediad of the shank with the 

 remainder, but to the lateral aspect, inserting as a caudal extension of 

 the superficial biceps. Accompanying the hypertrophy of the semitendi- 

 nosus is atrophy of the semimembranosus, which is a weak slip of a 

 muscle, some ten millimeters broad, beneath the other. 



There is a peculiar development of the sartorius. This arises from 

 the tip of the ilium, with origin extending broadly onto the ventral 

 border of the bone. As a broad, thin muscle it inserts for 40 mm. onto 

 the knee and a bit distad. In continuation still farther distad over the 

 proximal part of the medial shank is the insertion, for another 40 mm., 

 of the gracilis. 



The lumbar part of the erector spinae was very robust, the powerful 

 iliocostal part causing a flaring outward of the ilium, to which it is at- 

 tached. The hypaxial lumbar muscles were, however, definitely weak 

 and no larger than one would expect in any terrestrial mammal of equal 

 size. 



In considering the above muscles it cannot be claimed that any particu- 

 lar swimming method is clearly indicated. Because the interaction of the 

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