1 66 TOPOGRAPHIC AND APPLIED ANATOMY. 



tibia, from the interosseous membrane, and from the deep fascia, and runs to the inner margin 

 of the sole, where it is inserted upon the plantar surfaces of the internal cuneiform and of the 

 first metatarsal bones. (2) The extensor longus digitorum arises from the external tuberosity 

 of the tibia, from the interosseous membrane, from the fibula, and from the deep fascia, and 

 inserts by four tendons into the four outer toes ; a fifth tendon runs to the base of the fifth meta- 

 tarsal bone at the outer border of the foot (M. peroneus tertius). (3) The extensor longus 

 hallucis arises at a lower level from the interosseous membrane between the two former muscles 

 and runs to the second phalanx of the great toe. 



Each of the three muscles possesses an individual synovial sheath in the anterior annular 

 ligament at the ankle. 



II. Fibular Muscles. (i) The peroneus longus. The anterior portion of this muscle arises 

 from the external tuberosity of the tibia, from the head of the fibula, from the anterior intermus- 

 cular septum, and from the upper third of the anterior margin of the fibula; the posterior por- 

 tion arises from the fibula between the head and the lower third of the bone. The tendon runs 

 behind the external malleolus, through the groove of the cuboid bone, and passes obliquely 

 across the sole of the foot to the base of the first metatarsal bone. (2) The peroneus brevis, 

 which is covered by the preceding muscle, takes origin from the lower two-thirds of the fibula as 

 far down as the external malleolus. The tendon crosses that of the peroneus longus and inserts 

 into the tuberosity of the fifth metatarsal bone. The tendons of both peroneal muscles pass 

 through a common compartment behind the external malleolus (Fig. 88), in which situation they 

 are firmly held by two processes of the crural fascia designated as retinacula. 



Ill (a) Superficial Flexors (the muscles of the calf). (i) The gastrocnemius arises by two 

 heads from the bone above the femoral condyles; in the middle of the leg the muscle becomes 

 continuous with the tendo calcaneus (Achillis), which inserts into the tuberosity of the os calcis. 

 (2) The soleus, beneath the preceding muscle, arises from the head and upper third of the fibula 

 and from the oblique line of the tibia and runs downward into the tendo Achillis. (3) The 

 plantaris, like its analogue in the upper extremity, the palmaris longus, is an inconstant muscle. 

 It arises from the external condyle of the femur above the outer head of the gastrocnemius and 

 its tendon usually runs into the tendo Achillis. 



Ill (b) Deep Group 0} Flexors. (i) The popliteus runs from the external condyle of the 

 femur and the capsular ligament of the knee-joint to the posterior surface of the tibia as far down 

 as the oblique line. (2) The flexor longus digitorum springs from the posterior surface of the 

 tibia. Its tendon crosses to the outer side of the tibialis posticus, enters the sole of the foot, 

 passes beneath and is adherent to the tendon of the flexor longus hallucis, and divides into four 

 tendons for the four lesser toes. These tendons are inserted in a similar manner to those of the 

 flexor profundus digitorum in the hand. (3) The tibialis posticus arises from the interosseous 

 membrane and the adjacent portions of the tibia and fibula in the upper portion of the leg be- 

 tween the flexor longus digitorum and the flexor longus hallucis. Its tendon, with that of the 

 flexor longus digitorum, passes behind the internal malleolus to the inner aspect of the sole of the 

 foot, where it is inserted into the internal cuneiform and scaphoid bones. (4) The flexor longus 

 hallucis takes origin from the posterior surface of the lower two-thirds of the fibula and from the 

 posterior intermuscular septum. Its tendon runs in the posterior sulcus of the astragalus and 



