DR. J. MURIE ON THE ANATOMY OF THE SEA-LION. 569 
Biceps femoris.—Here enlarged to a remarkable degree, this muscle plays an important 
part in the peculiar movements of the hind legs. It may, indeed, be said to form 
the hinder half of the buttocks, which seem as if extended even backwards to the 
extremity of the lower leg. It is this curious shifting downwards of the insertions of 
muscles which gives the awkward gait to the hind limbs in land progression, while it 
adds power, and may be said to produce the long-lever screw-like movement of the 
after parts in natation. 
The biceps more or less continuous as a great dorsal sacro-tibial sheet of coarse 
muscular fibres, nevertheless indicates consistency of two portions—more, however, 
from the direction and overlapping of the fibres and points of insertion than in perfect 
separation into two elements. The united origin is over the caudal muscles and 
investing fascia of the dorsal region. A strong aponeurosis reaches from the third 
sacral spinous process to about the fifth caudal one; and from this the coarse fleshy 
fasciculi trend outwards, and terminate in a strong fascia, which reaches from the knee- 
joint to the ankle. ‘The thicker fibres of the anterior and somewhat smaller half (B,f", 
figs. 15 & 34) have a slight curve forwards and outwards, and are inserted by a strong, 
short tendon into the tuberosity of the outer condyle, close to the lower end of the shaft, 
and upwards from this along the outer line of the bone to near the great trochanter. 
Below the condyle the muscle is firmly fixed over the outer aspect of the knee-joint 
and tibio-fibular region downwards for its upper third. 
The so-named second, slightly larger portion of the biceps (Bi,f*) stretches over five 
caudal vertebre or thereabouts, the anterior border (median border) partially over- 
lapping the first portion of the biceps, the posterior border again overlapping the 
levator ani. As it comes towards the latter the caudal origin changes from the dorsal 
to the lateral surface of the vertebrae, continuous fascia, however, still overlapping the 
levatores caudz tendons. The attachment and insertion by aponeurotic fascia is along 
the lower and outer two thirds of the tibia, the fascia slanting below and being fixed 
into the fibular malleolus, where it joins the levator ani. 
Relations and Action. Both portions of the biceps partly cover the superior caudal 
muscles and tendons. The anterior half lies next the gluteus maximus, and overlies 
what appears to be the second portion of it. It is also superficial to the quadratus 
femoris, ischiatic nerves and vessels, and another abnormal deep obliquely set leg-muscle, 
the sacro-peroneus. It crosses the outer head of the gastrocnemius, peronsi, and is in 
close relation with the vastus externus. The hinder half covers the remainder of the 
sacro-peroneus and those of the calf; it is also in relation with the semimembranosus, 
a muscle here also peculiar in its relations. Functionally it is an adductor of the lower 
leg, flexor of the knee, and rotator outwards of the limb. 
The remarkable muscle which I term sacro-peronwus (Sp, figs. 34 & 35), is a thickish, 
flat, nearly uniformly broad band of fleshy fibres, which arises from the outside of the 
caudal muscles at the hinder end of the sacrum, occupying the surface of the superior 
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