254 POSTERIOR TIBIAL REGION. 



base of the second phalanx, and the two lateral slips are continued on- 

 wards, to be inserted into the base of the third. 



Relations. By its anterior surface with the deep fascia of the leg and 

 foot, and with the anterior annular ligament. By its posterior surface with 

 the interosseous membrane, fibula, ankle joint, extensor brevis digitorum 

 which separates its tendons from the tarsus, and with the metatarsus and 

 phalanges. By its inner surface with the tibialis anticus, extensor pro- 

 prius pollicis, and anterior tibial vessels. By its outer border with the 

 peroneus longus and brevis. 



The PERONEUS TERTIUS (flexor tarsi fibularis) arises from the lower 

 fourth of the fibula, and is inserted into the base of the metatarsal bone of 

 the little toe. Although apparently but a mere division or continuation 

 of the extensor longus digitorum, this muscle may be looked upon as 

 analogous to the flexor carpi ulnaris of the fore-arm. Sometimes it is alto- 

 gether wanting. 



The EXTENSOR PROPRIUS POLLICIS lies between the tibialis anticus and 

 extensor longus digitorum. It arises from the lower two-thirds of the 

 fibula and interosseous membrane. Its tendon passes through a distinct 

 sheath in the annular ligament, and is inserted into the base of the last 

 phalanx of the great toe. 



Relations. By its anterior surface, with the deep fascia of the leg and 

 foot, and with the anterior annular ligament. By its posterior surface, 

 with the interosseous membrane, the fibula, the tibia, the ankle joint, the 

 extensor brevis digitorum, and the bones and articulations of the great toe. 

 It is crossed upon this aspect by the anterior tibial vessels and nerve. By 

 its outer side, with the extensor longus digitorum, and in the foot with the 

 dorsalis pedis artery and veins ; the outer side of its tendon upon the dor- 

 sum of the foot being the guide to those vessels. By its inner side, with 

 the tibialis anticus, and with the anterior tibial vessels. 



Actions. The tibialis anticus and peroneus tertiiis are direct flexors of 

 the tarsus upon the leg; acting in conjunction with the tibialis posticus, 

 they direct the foot inwards, and with the peroneus longus and brevis, 

 outwards. They assist also in preserving the flatness of the foot during 

 progression. The extensor longus digitorum and 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 tne 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 (yao'T^oxv^fxiov, the bellied part of the leg) arises* 

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



