THE TIBIOFIBULAR ARTICULATION .341 



The capsular ligament (capsula articujarifi) consists of a membranous bag 

 which surrounds the articulation, being 'attached around the margins of the 

 articular facets on the tibia and fibula, and is much thicker in front than behind. 



The anterior superior ligament (Fig. 273) consists of two or three broad and 

 flat bands which pass obliquely upward and inward from the front of the head 

 of the fibula to the front of the outer tuberosity of the tibia. 



The posterior superior ligament (Fig. 266) is a single thick and broad band 

 which passes upward and inward from the back part of the head of the fibula 

 to the back part of the outer tuberosity of the tibia. It is covered by the 

 tendon of the Popliteus muscle. 



Synovial Membrane. A synovial membrane lines this articulation, which at its upper and 

 back part is occasionally continuous with that of the knee-joint. 



2. THE MIDDLE TIBIOFIBULAR LIGAMENT OR INTEROSSEOUS MEMBRANE 

 (MEMBRANA INTEROSSEA CRURIS) (Fig. 273). 



An interosseous membrane extends between the contiguous margins of the 

 tibia and fibula and separates the muscles on the front from those on the back 

 of the leg. It consists of a thin, aponeurotic lamina composed of oblique fibres 

 which for the most part pass downward and outward between the interosseous 

 ridges on the two bones; some few fibres, however, pass in the opposite direction, 

 downward and inward. It is broader above than below. Its upper margin 

 does not quite reach the superior tibiofibular joint, but presents a free concave 

 border, above which is a large, oval aperture for the passage of the anterior tibial 

 vessels forward to the anterior aspect of the leg. At its lower part is an opening 

 for the passage of the anterior peroneal vessels. It is continuous below with 

 the inferior interosseous ligament, and is perforated in numerous places for the 

 passage of small vessels. It is in relation, in front, with the Tibialis anticus, 

 Extensor longus digitorum, Extensor proprius hallucis, Peroneus tertius, and 

 the anterior tibial vessels and nerve; behind, with the Tibialis posticus and 

 Flexor longus hallucis. 



3. THE INFERIOR TIBIOFIBULAR ARTICULATION (SYNDESMOSIS TIBIOFIBULARIS) 



(Figs. 275, 276). 



This articulation is formed by the rough, convex surface of the inner side of 

 the lower end of the fibula, connected with a concave rough surface on the outer 

 side of the tibia. Below, to the extent of about one-sixth of an inch, these sur- 

 faces are smooth, and covered with cartilage, which is continuous with that of 

 the ankle-joint. The ligaments of this joint are: 



Anterior Inferior Tibiofibular. Transverse or Inferior. 



Posterior Inferior Tibiofibular. Inferior Interosseous. 



The anterior inferior ligament (ligamentum malleoli lateralis anterius) (Figs. 

 273 and 277) is a flat, triangular band of fibres, broader below than above, which 

 extends obliquely downward and outward, between the adjacent margins of the 

 tibia and fibula, on the front aspect of the articulation. It is in relation, in front, 

 with the Peroneus tertius, the aponeurosis of the leg, and the integument, ben hid, 

 with the inferior interosseous ligament; and lies in contact with the cartilage 

 covering the astragalus. 



