236 POSTERIOR TIBIAL REGION. 



extensor proprius pollicis, are direct extensors of the phalanges ; but 

 continuing their action, they assist the tibialis anticus and peroneus 

 tertius, in flexing the entire foot upon the leg. Taking their origin 

 from below, they increase the stability of the ankle-joint. 



Posterior tibial Region. 



Superficial Group. 



Gastrocnemius, 



Plantaris, 



Soleus. 



Dissection. Make an incision from the middle of the popliteal 

 space down the middle of the posterior part of the leg to the heel, 

 bounding it inferiorly by a transverse incision passing between the 

 two malleoli. Turn aside the flaps of integument and remove the 

 fasciae from the whole of this region; the gastrocnemius muscle will 

 then be exposed. 



The Gastrocnemius (/aoVgoxv^fjuov, the bellied part of the leg) arises 

 by two heads from the two condyles of the femur, the inner head 

 being the longest. They unite to form the beautiful muscle so cha- 

 racteristic of this region of the limb. It is inserted, by means of the 

 tendo Achillis, into the lower part of the posterior tuberosity of the 

 os calcis, a synovial bursa being placed between that tendon and 

 the upper part of the tuberosity. The gastrocnemius must be 

 removed from its origin, and turned down, in order to expose the 

 next muscle. 



Relations. By its superficial surface with the deep fascia of the 

 leg which separates it from the external saphenous vein, 'and with 

 the external saphenous nerve. By its deep surface with the lateral 

 portions of the posterior ligament of the knee-joint, the popliteus, 

 plantaris, and soleus. The internal head of the muscle rests against 

 the posterior surface of the internal condyle of the femur; the exter- 

 nal head against the outer side of the external condyle. In the lat- 

 ter a sesamoid bone is sometimes found. 



The Plantaris (planta, the sole of the foot), an extremely diminu- 

 tive muscle situated between the gastrocnemius and soleus, arises 

 from the outer condyle of the femur ; and is inserted, by its long and 

 delicately slender tendon, into the inner side of the posterior tube- 

 rosity of the os calcis, by the side of the tendo Achillis; having crossed 

 obliquely between the two muscles. 



The Soleus (solea, a sole) is the broad muscle upon which the 

 plantaris rests. It arises from the head and upper third of the fibula, 

 from the oblique line and middle third of the tibia. Its fibres con- 

 verge to the tendo Achillis, by which it is inserted into the posterior 

 tuberosity of the os calcis. Between the fibular and tibial origins of 

 this muscle is a tendinous arch, beneath which the popliteal vessels 

 and nerve pass into the leg. 



Relations. By its superficial surface with the gastrocnemius and 



