TIBIO-FIBULAR ARTICULATIONS. 163 



Jie folds in the interior of the joint, called "ligamentum mucosum," and 

 "ligamenta alaria." The superior pouch of the synovial membrane is 

 supported and raised during the movements of the limb by a small muscle, 

 the subcmreus, which is inserted into it. 



Between the ligamentum patellae and the synovial membrane is a con- 

 siderable mass of fat, which presses the membrane towards the interior of 

 the joint, and occupies the fossa between the two condyles. 



Besides the proper ligaments of the articulation, the joint is protected 

 on its anterior part by the fascia lata, which is thicker upon the outer than 

 upon the inner side, by a tendinous expansion from the vastus internus, 

 and by some scattered ligamentous fibres which are inserted into the sides 

 of the patella. 



Actions. The knee joint is one of the strongest of the articulations of 

 the body, while at the same time it admits of the most perfect degree of 

 movement in the directions of flexion and extension. During flexion, the 

 articular surface of the tibia glides forward on the condyles of the femur, 

 the lateral ligaments, the posterior, and the crucial ligaments are relaxed, 

 while the ligamentum patellaB being put upon the stretch, serves to press 

 the adipose mass into the vacuity formed in the front of the joint. In 

 extension, all the ligaments are put upon the stretch, with the exception 

 of the ligamentum patellae. When the knee is semi-flexed, a partial de- 

 gree of rotation is permitted. 



3. Articulation between the Tibia and Fibula. The tibia and fibula are 

 held firmly connected by means of seven ligaments, viz. 



Anterior, ) , Interosseous membrane, 



Posterior, \ a Interosseous inferior, 



Anterior, 5 , , Transverse. 

 Posterior, \ 



The anterior superior ligament is a strong fasciculus of parallel fibres, 

 passing obliquely downwards and outwards from the inner tuberosity of 

 the tibia, to the anterior surface of the head of the fibula. 



The posterior superior ligament is disposed in a similar manner upon 

 the posterior surface of the joint. 



Within the articulation there is a distinct synovial membrane which is 

 sometimes continuous with that of the knee joint. 



The interosseous membrane or superior interosseous ligament is a broad 

 layer of aponeurotic fibres which pass obliquely downwards and outwards, 

 from the sharp ridge on the tibia to the inner edge of the fibula, and are 

 crossed at an acute angle by a few fibres passing in the opposite direction. 

 The ligament is deficient above, leaving a considerable interval between 

 the bones, through which the anterior tibial artery takes its course for- 

 wards to the anterior aspect of the leg, and near its lower third there is 

 an opening for the anterior peroneal artery and vein. 



The interosseous membrane is in relation, in front, with the tibialis 

 anticus, extensor longus digitorum, and extensor proprius pollicis muscle, 

 with the anterior tibial vessels and nerve, and with the anterior peroneai 

 artery ; and behind, with the tibialis posticus, and flexor longus digitorum 

 muscle, and with the posterior peroneal artery. 



The inferior interosseous ligament consists of short and strong fibres, 

 which hold the bones firmly together inferiorly, where they are nearly n 



