132 TOPOGRAPHICAL ANATOMY OF 



becomes superficial about the middle of the leg. Its superficial course 



has already been examined. The distal muscular branch (ramus mus- 



cularis distalis) arises from the tibial nerve as this lies between the 



heads of the gastrocnemius muscle. It furnishes filaments to the 



gastrocnemius, soleus, plantaris, the flexors of the digit, and the 



popliteus. 



Dissection. — Reflect the plantaris muscle, and examine the deep 

 muscles of the leg. These are four in number, three of which (flexor 

 hallucis longus, flexor digitorum longus, and tibialis posterior) may be 

 grouped together as the deep flexor of the digit. 



M. flexor digitorum profundus. — The deep flexor of the digit is 

 divisible into three muscles, the tendons of which join into one in the 

 neighbourhood of the tarsus. 



(1) M. tibialis posterior. — The posterior tibial muscle is the most 

 superficial of the three component parts of the deep flexor. Its origin 

 is from the lateral condyle of the tibia and the head of the fibula. 

 About the junction of the middle and distal thirds of the tibia a 

 flattened tendon takes the place of the fleshy belly of the muscle and 

 joins the tendon of the flexor hallucis longus shortly before the end of 

 the tibia is reached. 



(2) M. flexor hallucis 1 longus. — This head of the deep flexor is much 

 stronger than the foregoing — with which it is more or less intimately 

 united — and contains a considerable proportion of tendinous tissue 

 interspersed among its fleshy bundles. It lies directly upon the tibia, 

 from the posterior surface and lateral condyle of which it rises, as well 

 as from the whole length of the fibula and the interosseous ligament. 

 A strong, rounded tendon, common to this and the foregoing muscle, 

 traverses the deep groove at the back of the tarsus, and later will be 

 followed down the metatarsus. It should be noticed that the common 

 tendon is exceedingly dense and partly cartilaginous where it plays 

 over the groove formed by the tuber and sustentaculum tali of the 

 calcaneus. 



(3) M. flexor digitorum longus. — The slender medial head of the 

 deep flexor is the most distinct, and lies in the groove between the 

 foregoing muscles and the popliteus. Its origin is from behind the 

 lateral condyle of the tibia. A slender, rounded tendon begins about 

 the middle of the tibia, traverses a groove provided with a synovial 

 sheath on the medial malleolus of the tibia, and joins the main tendon 

 of the deep flexor in the proximal third of the metatarsus. 



M. popliteus. — The triangular popliteal 2 muscle covers part of the 



1 Hallux [L.], the great toe. aA.Xoyu.ai (hallomai) [Gr.], to spring, leap, bound. 



2 Poplcs [L.], the ham or hough. (In the horse, the term hough or hock is used to 

 indicate the tarsal region, instead of the back of the femoro-tibial joint.) 



