628 DISSECTION OF THE LEG. 



to be traced to the ends of the digits. In the leg the anterior tibial nerve 

 and vessels are to be followed from the dorsum into their intermuscular 

 space, and are then to be cleaned as high as the knee. 



The anterior annular ligament consists of two parts, upper and lower, 

 which confine the muscles in their position : the former serving to bind 

 the fleshy parts to the bones of the leg, and the latter to keep down the 

 tendons on the dorsum of the foot : 



The upper part (fig. 215, 3 ), above the level of the ankle-joint, is at- 

 tached laterally to the bones of the leg ; it possesses one sheath with 

 synovial membrane for the tibialis anticus. 



The lower part is situate in front of the tarsal bones. It is inserted 

 externally by a narrow piece into the upper surface of the os calcis, in 

 front of the interosseous ligament ; and internally, where it is thin and 

 widened, into the plantar fascia and the inner malleous. In this piece of 

 the ligament there are three sheaths : an inner one for the tibialis anticus ; 

 an outer for the extensor longus digitorum and peroneus tertius ; and an 

 intermediate one for the extensor pollicis. Separate synovial membranes 

 line the sheaths. 



The external annular ligament is placed below the fibula, and is at- 

 tached on the one side to the outer malleolus, and on the other to the os 

 calcis. Its lower edge is connected by fibrous tissue to the sheaths of the 

 peronei muscles on the outer side of the os calcis. It contains the two 

 lateral peronei muscles in one compartment ; and this is lined by a syno- 

 vial membrane, which sends two offsets below into the sheaths of the 

 peronei muscles. 



The MUSCLES ON THE FRONT OF THE LEG (fig. 215) are three in num- 

 ber. The large muscle next the tibia is the tibialis anticus ; that next 

 the fibula, the extensor longus digitorum ; whilst a small muscle, appa- 

 rently the lower part of the last, with a separate tendon to the fifth meta- 

 tarsal bone, is the peroneus tertius. The muscle between the tibialis and 

 extensor digitorum, in the lower half of the leg, is the extensor pollicis. 



On the dorsum of the foot only one muscle appears, the extensor brevis 

 digitorum. 



The TIBIALIS ANTICUS (fig. 215, J ) reaches the tarsus: it is thick and 

 fleshy in the upper, but tendinous in the lower part of the leg. It arises 

 from the outer tuberosity and the upper half or more of the tibia ; from 

 the contiguous part of the interosseous ligament ; and from the fascia of 

 the leg and the intermuscular septum between it and the next muscle. 

 Its tendon begins below the middle of the leg, and passes through com- 

 partments in the pieces of the annular ligament, to be inserted into the 

 internal cuneiform bone, and the metatarsal bone of the great toe. 



The muscle is subaponeurotic. It lies at first outside the tibia, resting 

 on the interosseous membrane, but it is then placed, successively, over the 

 end of the tibia, the ankle-joint, and the inner tarsal bones. The outer 

 border touches the extensor muscles of the toes, and conceals the anterior 

 tibial vessels. 



Action. Supposing the foot not fixed, the tibialis bends the ankle, 

 moves the great toe towards tl.e middle line of the body, and raises the 

 inner border of the foot. 



If the foot is fixed it can lift the inner border with the tibialis posticus, 

 and support the foot on the outer edge. 



If the tibia is slanting backwards, as when the advanced limb reaches 

 the ground in walking, it can bring forwards and make steady that bone. 



