372 THE ARTICULATIONS. 



also sends off two fringe-like folds, called the ligamenta alaria, which extend from 

 the sides of the ligamentum mucosum, upward and laterally between the patella 

 and femur. On either side of the joint it passes downward from the femur, lining 

 the capsule to its point of attachment to the semiluriar cartilages ; it may then be 

 traced over the upper surfaces of these cartilages to their free borders, and from 

 thence along their under surfaces to the tibia. At the back part of the external 

 one it forms a cul-de-sac between the groove on its surface and the tendon of the 

 Popliteus ; it surrounds the crucial ligaments and lines the inner surface of the 

 ligaments which enclose the joints. The pouch of synovial membrane between 

 the Extensor tendon and front of the femur is supported, during the movements 

 of the knee, by a small muscle, the Subcrureus, which is inserted into the upper 

 part of the capsular ligament. 



The folds of synovial membrane and the fatty processes contained in them act, 

 as it seems, mainly as padding to fill up interspaces and obviate concussions. 

 Sometimes the bursa beneath the Quadriceps extensor is completely shut off from 

 the rest of the synovial cavity, thus forming a closed sac between the Quadriceps 

 and the lower part of the front of the femur, or it may communicate with the 

 synovial cavity by a minute aperture. 



The bursse about the knee-joint are the following : 



In front there are three bursse : one is interposed between the patella and the 

 skin ; another, of small size, between the upper part of the tuberosity of the tibia 

 and the ligamentum patellae ; and a third between the lower part of the tuberosity 

 of the tibia and the skin. On the outer side there are four bursse : (1) one beneath 

 the outer head of the Gastrocnemius (which sometimes communicates with the 

 joint); (2) one above the external lateral ligament between it and the tendon of 

 the Biceps ; (3) one beneath the external lateral ligament between it and the ten- 

 don of the Popliteus (this is sometimes only an expansion from the next bursa) ; 

 (4) one beneath the tendon of the Popliteus between it and the condyle of the femur, 

 which is almost always an extension from the synovial membrane. 



On the inner side there are five bursse : (1) one beneath the inner head of the 

 Gastrocnemius, which sends a prolongation between the tendons of the Gastro- 

 cnemius and Semimembranosus : this bursa often communicates with the joint; 

 (2) one above the internal lateral ligament between it and the tendons of the 

 Sartorius, Gracilis, and Semitendinosus ; (3) one beneath the internal lateral 

 ligament between it and the tendon of the Semimembranosus : this is sometimes 

 only an expansion from the next bursa ; (4) one beneath the tendon of the Semi- 

 membranosus, between it and the head of the tibia ; (5) sometimes there is a bursa 

 between the tendons of the Semimembranosus and of the Semitendinosus. 



Structures around the Joint. In front and at the sides, the Quadriceps exten- 

 sor ; on the outer side, the tendons of the Biceps and the Popliteus and the 

 external popliteal nerve ; on the inner side, the Sartorius, Graxnlis, Semitendinosus, 

 and Semimembranosus ; behind, an expansion from the tendon of the Semimembra- 

 nosus, the popliteal vessels, and the internal popliteal nerve, Popliteus, Plantaris, 

 and inner and outer heads of the Gastrocnemius, some lymphatic glands, and 

 fat. 



The Arteries supplying the joint are derived from the anastomotica magna 

 branch of the femoral, articular branches of the popliteal, anterior and posterior 

 recurrent branches of the anterior tibial, and descending branch from the external 

 circumflex of the Profunda. 



The Nerves are derived from the obturator, anterior crural, and external and 

 internal popliteal. 



Actions. The knee-joint permits of movements of flexion and extension, and, 

 in certain positions, of slight rotation inward and outward. The movement of 

 flexion and extension does not, however, take place in a simple, hinge-like man- 

 ner, as in other joints, but is a complicated movement, consisting of a certain 

 amount of gliding and rotation ; so that the same part of one articular surface is 

 not always applied to the same part of the other articular surface, and the axis 



