452 DR. J. MURIE ON THE ANATOMY OF THE WALRUS. 
Although the caudo-tibial expansion is very considerable and powerful in Trichechus, 
the muscular fibres of the levator ani are notwithstanding less developed than in 
O. jubata. In the place of muscle there is substituted a larger quantity of ligamentous- 
like substance or fascia, with, comparatively speaking, few fleshy fibres sparsely inter- 
mixed. Moreover the increased development of the aponeurosis continuous with the 
panniculus carnosus gives the caudo-tibial or astragaloid extension great elasticity and 
strength, whilst its breadth leaves less of the tail free than is the case in Phoca and 
Otaria. 
Superficial veins homologous with the saphenous of other mammals lie upon and 
pierce the membrane above spoken of. 
Muscles of the Pelvic Limb. 
The gluteal muscles, as in Ofaria, are relatively small. The gluteus maximus does 
not show any distinct line of separation into two parts in the Walrus, as to some extent 
it does in the other genus. It is comparatively larger than in the latter, and, though 
thinner than the gluteus medius, is the broader of the two and partially overlaps it. 
‘Thus its spinal origin by fascia extends for the whole length of the sacrum. 
The gluteus medius does not overlap the gluteus maximus at any part, nor does it 
form to the same extent that encircling sheath to the gluteus minimus which obtains 
in the Sea-lion; in other respects it agrees with that of the latter animal, excepting no 
fixed attachment to the inferior border of the ilium. As may be inferred, the gluteus 
minimus occupies the whole of the outer surface of the ilium. 
In the Walrus the biceps femoris presents the same broad, coarse, muscular sacro- 
tibial sheet met with in the Sea-lion, Its anterior border, however, does not overlap 
the gluteus maximus; and its first portion or half has origin by fascia, interspersed with 
muscular fibre, from the fifth or last sacral and the three next caudal spinous processes. 
The posterior half does not, as in Ofaria, have origin above the supracaudal muscles, 
but instead arises from the tips of the transverse processes of the six anterior caudal 
vertebre ; and a considerable portion of it is overlapped by the first half of the muscle. 
The femoral and tibial insertion and the relations to other muscles are identical. 
The following muscles of the leg offer no differences worthy of mention from those 
of Otaria jubata:—Pectineus, rectus femoris, the vasti and crureus, soleus, tibialis 
anticus, extensor proprius hallucis, extensor communis digitorum, peroneus longus, 
peroneus quinti, flexor longus digitorum, and the flexor longus hallucis. 
Others show little variation. For example, the gracilis (Pl. LV. fig. 25, Gr) has no 
corner covering the insertion of the external oblique at the symphysis; and its tibial 
attachment is greater; namely, it extends almost the entire length of the tibia. The 
double adductors, longus and magnus, as described in Ofaria, present no clear line of 
demarcation in the Walrus, but in the latter the femoral vessels and nerves pierce the 
adductor longus as well as adductor magnus, 
