138 



MUSCLES OF THE LEG. 



nteriorly, with the fibula and interosseous 

 ligament posteriorly, with the peronens brevis 

 on the fibular side, and with the extensor com- 

 munis on the tibial side. Its tendon passes in 

 the same sheath with that of the common ex- 

 tensor, under the annular ligament. 



A very slight effort of the extensor com- 

 nnmis and extensor proprius pollicis extends 

 the digital phalanges, and, if their action be 

 continued, they will be made to bend the foot 

 upon the leg. This they are enabled to do by 

 the manner in which their line of direction is 

 altered by the annular ligament of the ankle- 

 joint, as it gives them all the mechanical ad- 

 vantage of a pulley. The tibialis anticus and 

 the peroneus tertius are the direct flexors of the 

 foot on the leg, and if either act separately, it 

 will give a slight inclination towards the cor- 

 responding side, and thus the last-named 

 muscle forms one of that important set whose 

 action is, by elevating the outer side of the 

 foot, to throw the weight of the body on the 

 inner side.* In the erect position these muscles 

 take their fixed point below, and, by drawing 

 on the bones of the leg, keep them perpen- 

 dicular on the foot. 



The external muscles of the leg are two, the 

 peroneus longus and brevis. They occupy the 

 whole length of the outer side of the fibula, and 

 are placed between the extensors and flexors. 



1. Peroneus longus is a long powerful muscle, 

 arising from a small portion of the fibular side 

 of the head of the tibia, from the upper third 

 of the outer side of the fibula, and from the 

 fascia of the leg and its intermuscular pro- 

 cesses. Proceeding obliquely downwards, the 

 fibres are attached to a strong tendon, which 

 passes, in contact with the peroneus brevis, 

 along a groove at the back of the outer mal- 

 leolus, enclosed in a synovial sheath. The 

 tendon then passes through a deep sulcus in 

 the cuboid bone, behind the base of the meta- 

 tarsal bone of the little toe, winding obliquely 

 across the sole of the foot, covered by the 

 muscles of this part, till it is inserted into the 

 internal cuneiform bone and base of the meta- 

 tarsal bone of the great toe. In the tendon 

 opposite the cuboid bone, is usually found a 

 sesamoid bone. A bursal sheath encloses it in 

 its passage across the foot. The action of this 

 important muscle is to assist in extending the 

 foot upon the leg, but principally to elevate 

 the outer side of the foot, and thus regulate 

 the bearing of the leg so as to throw the prin- 

 cipal part of the weight upon the great toe.f 



This muscle is in contact on its outer side 

 with the fascia of the leg. Indeed this apo- 

 neurosis almost invests it, dipping between it 

 and the flexor behind and extensors before. 

 The peroneus is in contact with the fibula on 

 its inner side above, lower down it rests upon 

 the peroneus brevis. When passing across the 

 foot it lies close to the bones, and conse- 

 quently is covered by all the muscles of the 

 sole. 



2. Peroneus brevis is situated at the outer 



* For further observations upon the action of the 

 peronei muscles, see article FOOT, MUSCLES OF. 

 f See also Quain's Manual of Anatomy. 



side of the leg, but lower down as to its at- 

 tachments than the preceding muscle. It arises 

 fleshy from the lower half of the outer side of 

 the fibula to near the outer malleolus. It 

 sends off a roundish strong tendon, which passes 

 in the same groove behind the outer malleo- 

 lus, and in the same synovial sheath as the pre- 

 ceding muscle, but after passing the malleolus 

 it has a sheath proper to itself. It is inserted 

 into the base of the metatarsal bone of the 

 little toe. Connected on its outer side to the 

 peroneus longus, on the inner side to the fibula, 

 anteriorly to the common extensor and pero- 

 neus tertius, and posteriorly to the flexor longus 

 pollicis. 



The action of these two muscles is peculiar. 

 By the change in their direction, after turning 

 behind the outer ankle, they are enabled to 

 draw the foot back, and so extend it on the 

 leg ; 



The penoneus tertius is on the contrary a 

 flexor ; it lies before the fibula, and combines 

 in this action with the tibialis anticus to assist 

 the flexor. When, however, the three peronei 

 act together, and without the other flexors, their 

 combined action is to evert the sole of the foot, 

 and thus counterbalance the effect of the feeble- 

 ness of the outer side of the foot by trans- 

 ferring the superincumbent weight to the inner 

 side. This action is particularly exemplified 

 in skaiting, but it is essential to every move- 

 ment of ordinary progression. (See article 

 FOOT, MUSCLES OF.) "When the foot is the 

 fixed point, the peronei act by keeping the 

 fibula and the whole leg steady, and thus, as 

 in the act of standing on one foot, counter- 

 acting the tendency of the body to fall in- 

 wards. 



The posterior region of the leg comprises 

 seven muscles, six of which are acting on the 

 foot and toes, and one is proper to the knee- 

 joint. We shall examine them as they are met 

 with in dissection, and shall therefore describe 

 them as forming two layers, superficial and 

 deep. The first contains three muscles: 1. gas- 

 trocnemius; 2. soleus ; 3. plantaris. 



1. Gastrocnemius. This is situated imme- 

 diately under the aponeurosis, and is a power- 

 ful muscle, broad and flat anteriorly, and con- 

 vex posteriorly, and forming the greater part 

 of what is called the calf. It arises by two 

 distinct heads from the back and upper part 

 of the two condyles of the femur, of which 

 the inner is the longer, and somewhat larger. 

 These heads have between them a broad 

 sulcus, which forms the lower part of the pop- 

 liteal space. They unite a little below the 

 knee-joint, in a middle tendinous line, and 

 below the middle of the tibia send off a flat 

 tendon which unites with the tendon of the 

 soleus, a little above the ankle. 



The posterior surface is covered by the fascia 

 of the leg ; anteriorly it rests upon the popli- 

 teus, soleus, and plantaris, and popliteal 

 vessels. When its heads pass over the cun- 

 dyles of the femur, they are guarded by synovial 

 bursre. 



2. Soleus. This is the second portion of 

 that great muscle of the leg which has been 



