“named by Meckel the friceps sure. It is 
seen immediately on raising the last muscle. 
It arises from two distinct situations ; first, from 
the upper and back part of the head of the 
fibula, and from the posterior surface and outer 
\dge of that bone for some way down. Se- 
cond, from the oblique ridge on the posterior 
' surface of the tibia, just below the popliteus, 
“and from the inner edge of that bone during 
‘the middle third of its length. From these 
two attachments the muscle almost imme- 
diately forms a thick fleshy belly, which de- 
sends lower than the gastrocnemius before it 
ends off its tendon. This, which is flat and 
ong, soon unites to the tendon of the gastro- 
“enemius to form the tendo Achillis,and is then 
passing to be inserted into the upper and 
back part of the projecting portion of the 
os calcis. At its insertion there is a small 
bursa between the upper part of the bone and 
the tendon. 
_ The soleus is in contact with the gastro- 
cnemius posteriorly ; below its fleshy fibres ap- 
— on each side of the tendon of that muscle. 
tween its two origins the posterior tibial 
vessels and nerve are passing, defended from 
pressure by the tendinous expansion which is 
on the under side of the muscle, and which 
spreads across from tibiato fibula. This muscle 
| is also in contact with the plantaris, the tendon 
of which crosses it obliquely from without 
| to within. In front it rests upon the deep 
layer of muscles and upon the posterior tibial 
vessels. 
_ The tendo Achillis is the thickest and 
strongest tendon in the body; it tapers down- 
wards nearly to the heel, and _ before its 
‘attachment expands again a little. It lies 
| immediately under the skin, and between it 
and the bones is a considerable layer of cel- 
lular tissue containing fat. 
The action of the two last described muscles 
_ is to elevate the os calcis, and thereby to lift 
p the whole body. When this is done on 
_ one foot in the act of progression, the other is 
‘capable of being carried forward unimpeded 
| by the irregularities of the surface. When the 
foot is the fixed point, the soleus by acting on 
the tibia and fibula fixes the leg, while the 
| gastrocnemius: fixes the femur, or by acting 
| further, draws it backward so as to bend the 
_ knee and lower the body. 
| 3. Plantaris—This little muscle is entirely 
covered by the outer head of the gastro- 
| cnemius. It arises from the upper part of the 
external condyle of the femur, and from the 
" posterior ligament of the knee-joint. Its mus- 
a ular structure is only about two inches in 
‘length, and it sends its long slender tendon 
_ downwards and inwards, between the two great 
0 uscles of the calf, emerging from between 
them just where their two tendons unite; it 
then passes down in contact with the edge of 
‘the tendo Achillis, to be inserted into the heel 
at the inner side of that tendon. 
_ The action of the plantaris is to assist the 
great extensors of the foot, and to draw upon 
the capsule of the knee-joint, so as to prevent 
any ill effects upon that ligament from the 
; 
| 
4 
i 
{ 
SL 
MUSCLES OF THE LEG. 
139 
motions of the knee-joint. It is occasionally 
deficient. 
The deep layer of muscles consists of four : 
1. popliteus; 2. flexor longus digitorum; 3. 
flexor longus pollicis; 4. tibialis posticus. 
They lie in close contact with the bones, and 
the last three of them are covered by the deep 
fascia of the leg. 
This membrane is a thin expansion, dense 
in structure, connected on each side with the 
borders of the bones, and towards the ankles 
with the sheaths of the tendons ; and if traced 
along the interval between the inner ankle and 
the heel, it will be found to cover the vessels 
and to terminate at the internal annular liga- 
ment. Immediately underneath it we find 
the deep layer of muscles now under consi- 
deration. ~ 
1. Popliteus is situated below and behind 
the knee-joint, is flat and somewhat triangular, 
being broader below than above.  Arises 
within the capsular ligament of the knee-joint, 
by a round tendon, from the under and back 
part of the outer condyle of the femur; ad- 
heres to the posterior and outer surface of the 
external semilunar cartilage; perforates the 
back part of the capsular ligament, and forms 
a fleshy belly which runs obliquely downwards 
and inwards. It is covered by a thin tendi- 
nous fascia from the tendon of the semi-membra- 
nosus ; inserted broad, thin, and fleshy into an 
oblique ridge on the posterior surface of the 
tibia, a little below its head, and into the trian- 
gular space above that ridge. Action, to bend 
the knee-joint, and when bent, to roll it so as 
to turn the toes inwards. 
2. Flexor longus digitorum is thin and 
pointed at its commencement, but gradually 
increases, and then diminishes again as its 
fibres end in a tendon. Arises fleshy from 
the posterior flattened surface of the tibia, be- 
tween its internal and external angles, be- 
low the attachment of the soleus, and con- 
tinues to arise from the bone to within two or 
three inches of the ankle. The fibres run 
obliquely into a tendon, which is situated on 
the posterior edge of the muscle. This tendon 
runs in a groove of the tibia, behind the inner 
ankle, and then passing obliquely forwards 
into the sole of the foot, receives in its passage 
a strong slip from the tendon of the flexor longus 
pollicis. It then divides into four tendons, 
which pass through the slits in the tendons of the 
flexor brevis digitorum, and as they run along 
the under surface of the toes they are bound 
down by strong fibrous sheaths, within which 
there are also little accessory ligaments assist- 
ing in fixingthem. They are inserted into the 
bases of the extreme phalanges of the four 
lesser toes. The action of this muscle is to 
flex all the four smaller toes, and to assist in 
elevating the foot upon the toes. 
Previously to its division, the tendon of the 
flexor longus gives insertion to an accessory 
muscle of considerable power (flexor acces- 
sorius ), which connects it to the calcaneum, 
and materially modifies the direction of its 
action upon the toes. Close to the point of 
division, the tendons give origin to four small 
