576 DR. J. MURIE ON THE ANATOMY OF THE SEA-LION. 
Action. The broad single femoral origin of this muscle and its comparative 
obliquity of belly have a remarkable influence on its use. Thus it drags the os calcis 
inwards, and in so doing prepares the foot (semitwisted) to be thrown forwards, the 
inner margin being partly raised, so that the long hallux does not catch the ground 
until the after part of the foot has first touched it. While this takes place, the long 
extensor muscles are tense. 
Popliteus.—Proportionally this is a very large muscle. It arises from the outer 
condyle of the femur, but chiefly from the capsular ligament of the knee-joint by a 
short aponeurotic tendon. Becoming fleshy and of considerable breadth, it rolls round 
behind the head of the tibia, and is inserted into the inner edge of the upper half of 
that bone. The popliteus passes above the head of the fibula, and not crossing over it. 
Its fibres reach no further than the internal lateral ligament of the knee-joint (Po, 
fig. 37), which latter passes downwards and over it about the central line of the tibia. 
Action. A powerful rotator of the tibia inwards. The tendon of origin of the 
popliteus greatly strengthens the posterior ligament of the knee-joint, which is weak 
outside, 
The soleus (So) is represented by a large, fleshy, broad, thick, longitudinally trian- 
gular and flattened muscle. It is attached the whole length of the fibula and into the 
os calcis, which is drawn towards the fibula. ‘The upper half of the soleus arises from 
the fibula by a very strong aponeurotic fascia, which becomes fleshy and gradually 
thickens towards the free edge of the muscle, the fibres being directed downwards and 
backwards. At the lower end the muscle is wonderfully enlarged and leaves no space 
between the fibula and the os calcis. The tendinous superficies of the insertion of the 
soleus is outwards, the inner fleshy insertion reaching well round the inner side of the 
os calcis. A bursa exists at the extremity of the os calcis. A slip of this muscle takes 
origin from the outer condyle of the femur along with the popliteus muscle, 
Action. The soleus must exert considerable influence on the rotation of the foot 
inwards, as from its high origin outwardly and muscular belly rolling round inwardly, 
attached to the entire end of the os calcis, a lever of great power is obtained. 
The tibialis posticus (T.p, figs. 36 & 38) is of moderate size. It arises fleshy from the 
upper half of the interosseous interspace and membrane, and from the neighbouring 
parts of the tibia and lower three fourths of the fibula, and it partly passes between the 
bones in front and to the outer side of the tibia. Passing obliquely inwards and down- 
wards, it becomes tendinous only at the inner malleolus, where it glides through the 
innermost groove behind the malleolus; the tendon continues on the inner edge of the 
sole, to be inserted into the scaphoid bone. A powerful abductor inwards of the foot. 
The plantaris (Pla) is of considerable dimensions. Its fleshy origin is the outer 
condyle of the femur, along with the popliteus. It forms a muscular belly fully half as 
large as that of the gastrocnemius, and equally thick. This lies upon the soleus, and 
is partially covered by the belly of the gastrocnemius, its position being towards the 
