ANATOMY OF THE KNEE-JOINT. 227 



outwards and downwards. It assumes tliis position under 

 the action of the lower portion of the vastus interaus, wliich 

 may now be considered as an adductor patellai. It will be 

 observed also, that the passage fonvards of the lower end of 

 the ileo-tibial band, and the consequent slackening of the 

 external retinaculum, permits the bone to take up this internal 

 position. In consequence, therefore, of the movements of the 

 patella, in harmony with the oblique rotations of the knee- 

 joint, the bone, under the influence of its external retinaculum, 

 and of the lower part of the vastus internus, describes a curved 

 path, the concavity of which is directed upwards and outwards. 

 It is also guided in this path by the form and direction of the 

 femoral trochlea, and particularly by its upper and outer 

 portion, which, as is well known, projects considerably 

 upwards, forwards, and inwards, so as to convey the patella 

 to the inner side. 



The spaces, which would otherwise be produced by the 

 recession of certain parts of the cartilaginous surfaces from 

 one another in the movements of some joints, are occu- 

 pied by movable and yielding structures of two kinds — 

 interarticular fibro-cartilages, and the so-called Haversian 

 glands, wliich may be denominated synovial pads. The for- 

 mer occur when resistance to pressure is to be provided, the 

 latter when space is only to be occupied. The semilimar 

 fibro-cartilages of the knee belong to the former category : 

 and the brothers Weber have pointed out generally how 

 these elastic crescentic masses move backwards and for- 

 wards in the flexion and extension of the joint. But Meyer 

 has indicated with greater precision their peculiar functions. 

 The external semilunar cartilage must be viewed as an ap- 

 pendage to the external condyle of the femur, with which it 

 moves backwards in flexion, forwards in extensioiL These 

 movements are facilitated by its circular form, the approxi- 

 mation of its horns, its non-attachment to the anterior external 



