152 ARTHROLOGY, OR ANATOMY OF ARTICULATIONS 



to the front of the outer tuberosity of the tibia; some fibers 

 of the peroneus longus and extensor longus digitorum arise 

 from it. The posterior ligament connects the bones in a similar 

 manner, and is covered by one head of the soleus. This joint 

 cavity may communicate with the knee-joint. Fat fills the 

 space between the capsule and interosseous membrane. 



The joint surfaces move in a transverse and sagittal direc- 

 tion, more in the former; the purpose of the movement is 

 to allow a gliding at the low r er ends of the bones. This is an 

 arthrodial joint. 



The Interosseous Membrane 



Between the bones is the interosseous ligament or membrane, 

 its fibers passing down and out to the fibula; it separates the 

 flexor from the extensor muscles. Above is an opening for 

 the anterior tibial vessels, and below another for the anterior 

 peroneal. Close to the upper tibiofibular joint is a band of 

 fibers analogous to the oblique ligament of the forearm, running 

 in a direction opposite to that of the fibers of the rest of the 

 membrane. If the forearm be pronated and compared with 

 the leg, the two interosseous ligaments run in parallel directions. 



The Inferior Tibiofibular Joint 



The inferior tibiofibular joint presents interosseous, anterior, 

 posterior, and transverse ligaments. The interosseous is con- 

 tinuous with the interosseous membrane above. The anterior 

 and posterior ligaments connect corresponding surfaces of the 

 two bones. The transverse is under the posterior ligament, 

 projects below and connects the margins of the bones, and 

 forms part of the articulating surface for the astragalus. This 

 is an arthrodial joint. 



The Ankle-joint 



The tibiotarsal articulation is a ginglymus, or hinge joint, 

 formed by the lower extremity of the tibia and its malleolus 

 and the external malleolus of the fibula, the former articulating 

 with the upper convex surface and internal articular facet of 

 the astragalus; the latter, with the external articular facet of the 

 astragalus. 



