THE KNEE-JOINT 331 



II. The Knee-joint (Articulatio Genu). 



The knee-joint was formerly described as a ginglymus or hinge-joint, but is 

 really of a much more complicated character. It must be regarded as consist- 

 ing of three articulations in one one between each condyle of the femur and the 

 corresponding tuberosity of the tibia, which are condyloid joints, and one between 

 the patella and the femur, which is partly arthroidal, but not completely so, since 

 the articular surfaces are not mutually adapted to each other, so that the movement 

 is not a simple gliding one. This view of the construction of the knee-joint 

 receives confirmation from the study of the articulation in some of the lower 

 mammals, where three synovial membranes are sometimes found, corresponding 

 to these three subdivisions, either entirely distinct or only connected by small 

 communications. This view is further rendered probable by the existence of 

 the two crucial ligaments within the joint, which must be regarded as the external 

 and internal lateral ligaments of the inner and outer joints respectively. The 

 existence of the ligamentum mucosum would further indicate a tendency to sepa- 

 ration of the synovial cavity into two minor sacs, one corresponding to each joint. 



The bones entering into the formation of the knee-joint are the condyles of the 

 femur above, the head of the tibia below, and the patella in front. The bones are 

 connected by ligaments, some of which are placed on the exterior of the joint, 

 while others occupy its interior. 



External Ligaments. Interior Ligaments. 



Capsular. Anterior, or External Crucial. 



Anterior, or Ligamentum Patellae. Posterior, or Internal Crucial. 



Posterior. Two Semilunar Fibrocartilages. 



Internal Lateral. Transverse. 



Two External Lateral. Coronary. 



The capsular ligament (capsula articidaris} (Fig. 266) consists of an exceedingly 

 thin, but strong, fibrous membrane, which is strengthened in almost its entire 

 extent by heavy bands which are inseparably connected with it. In front it blends 

 with and forms part of the lateral patellar ligaments and fills in the interval 

 between the anterior and lateral ligaments of the joints, with which latter structures 

 it is closely connected. It is deficient above the joint and beneath the tendon of 

 the Quadriceps extensor. Behind, it is formed chiefly of vertical fibres, which 

 arise above from the condyles and intercondyloid notch of the femur, and is con- 

 nected below with the back part of the head of the tibia, being closely united 

 with the origins of the Gastrocnemius, Plantaris, and Popliteus muscles. It 

 passes in front of, but is inseparably connected with, the posterior ligament. 



The anterior ligament, or ligamentum patellae (Figs. 266, 270, and 271), is the 

 central portion of the common tendon of the Extensor muscles of the thigh, which 

 is continued from the patella to the tubercle of the tibia, supplying the place of 

 an anterior ligament. It is a strong, flat, ligamentous band about three inches in 

 length, attached, above, to the apex of the patella and to the rough depression on 

 its posterior surface; below, to the lower part of the tubercle of the tibia, its super- 

 ficial fibres being continuous over the front of the patella with those of the tendon 

 of the Quadriceps extensor. The lateral portions of the tendon of the Extensor 

 muscles in conjunction with the fascia lata pass down on either side of the patella, 

 and are attached to the tibia on either side of the tubercle; these are termed 

 lateral patellar ligaments (retinaculum patellae mediale et laterale), and merge 

 into the capsule. The posterior surface of the ligamentum patellae is separated, 



