THE LEG 367 



annular ligament), which crosses the interval between the 

 medial malleolus and the calcaneus, and, on the lateral side, 

 with the superior peroneal retinaculum which extends from 

 the lateral malleolus to the calcaneus. On the medial side 

 the deep fascia is attached to the medial border of the tibia, 

 where it blends with the periosteum on the medial surface of 

 that bone, and on the lateral side it joins the posterior fibular 

 intermuscular septum, by which it is attached to the lateral 

 crest of the fibula (Figs. 152, 155), thus it forms the posterior 

 boundary of the great posterior osteo-fascial compartment of 

 the leg. 



Posterior Osteo-fascial Compartment of the Leg. The posterior 

 osteo-fascial compartment of the leg is bounded, posteriorly, by the deep 

 fascia and, anteriorly, by the tibia, the interosseous membrane, and the 

 fibula. It contains the muscles, vessels, and nerves of the back of the leg, 

 and is divided into three portions by two fascial partitions which stretch 

 across it. The first partition is attached, medially, to the popliteal line of 

 the tibia (Fig. 152), and to the distal two-thirds of the medial border of the 

 tibia, and, laterally, to the posterior surface of the fibula, below the attach- 

 ment of the soleus, and to the lateral crest of the fibula (Fig. 152). Its 

 upper portion forms a fibrous arch which covers the terminal part of the 

 popliteal artery, and, in the distal part of the leg, it blends with and 

 plays a very important part in the formation of the laciniate ligament. It 

 separates the gastrocnemius, soleus, and plantaris, which lie in the posterior 

 portion of the osteo-fascial compartment, from the flexor digitorum longus, 

 the flexor hallucis longus, the tibial nerve and the posterior tibial artery 

 and its branches which lie in the middle area. 



The second septum, known as the fascia covering'the tibialis posterior, 

 is attached, medially, to the proximal part of the popliteal line of the tibia 

 and to the vertical ridge on the posterior surface of the tibia and, laterally, 

 to the medial crest of the fibula. Above, it blends with the interosseous 

 membrane, and below it fuses with the deep surface of the first septum in 

 the distal part of the leg. It separates the structures in the middle 

 part of the osteo-fascial compartment from the tibialis posterior which 

 occupies the anterior section of the compartment. Parts of the flexor 

 hallucis longus and the flexor digitorum longus arise from its posterior 

 surface, and fibres of the tibialis posterior spring from its anterior surface. 



It follows, from what has been stated, that the great posterior osteo- 

 fascial compartment of the leg is divided into three sections posterior, 

 middle, and anterior. The posterior section is bounded behind by the 

 deep fascia of the leg and in front by the first septum. It contains the 

 gastrocnemius, the soleus, the plantaris, which are called the superficial 

 muscles of the calf, and the tendo calcaneus, which is the common tendon 

 of insertion of the gastrocnemius and the soleus. 



The middle section is bounded posteriorly by the first septum and 

 anteriorly by the medial part of the tibia, the second septum, and the 

 posterior surface of the fibula. It contains the long flexor of the toes, the 

 long flexor of the great toe, the tibial nerve and its branches, and the 

 posterior tibial vessels and their branches and tributaries. 



The anterior section of the compartment is bounded posteriorly by the 

 second fascial septum, and anteriorly by the tibia and the interosseous 

 membrane. It contains the tibialis posterior muscle (Fig. 142). 



