MUSCLES OF THE LEG. 



139 



named by Meckel the triceps sura:. 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 

 edge 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- 

 scends lower than the gastrocnemius before it 

 sends off its tendon. This, which is fiat and 

 strong, soon unites to the tendon of the gastro- 

 cnemius 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- 

 pear on each side of the tendon of that muscle. 

 Between 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 tibia to 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 

 up 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- 

 cular structure is only about two inches in 

 length, and it sends its long slender tendon 

 downwards and inwards, between the two great 

 muscles 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 



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 fixing them. 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 ucces- 

 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 



