THE JOINTS. 53 



The wrist-joint is a hinge-joint, moving backwards and forwards, 

 and also allowing the hand to be moved a little edgewise out- 

 wards or inwards. The lower end of the radius forms a socket in 

 which the two uppermost bones of the wrist move, united so as to 

 form an oblong ball. Two lateral ligaments confine the hand to 

 the lower ends of the radius and ulna, and the whole joint is lined 

 by a synovial membrane. This joint is never dislocated, but it is 

 liable to sprains, and to disease, producing occasionally the loss of 

 the hand. 



The bones in the hand are not subject to dislocations, except at 

 the joint between the first and second pieces of the thumb a seem- 

 ingly trifling affair, but one which is extremely difficult to set to 

 rights ; so much so, that many of those who are the subjects of the 

 accident continue to go with the point of the thumb bent back, all 

 the rest of their days. 



The only dislocation that takes place in the spine is that between 

 the first and second vertebrae of the neck, in consequence of de- 

 struction of a ligament which keeps them in their places. When 

 this happens, the weight of the head makes it fall forward, carrying 

 the first vertebra with it, and the spinal marrow is so nipt between 

 it and the second, that the sufferer dies as surely and as instantane- 

 ously as if his neck were severed by the axe of the executioner. 



The hip-joint consists of a deep socket, formed by the ilium 

 above, ischium lower, and pubes before, into which the round head 

 of the femur or thigh-bone is set. The opposed surfaces are 

 covered with cartilage, and are tied together by an internal liga- 

 ment. A capsular ligament of great strength, attached round the 

 edge of the socket and to the neck of the bone, fixes it in its place. 

 The whole is lined by a synovial membrane. The joint is, not- 

 withstanding its strength, subject to dislocations, principally on 

 account of the long lever which the thigh-bone affords to any force 

 acting upon it, so as to tear the head from its socket. 



The knee is the most complicated joint in the whole body. The 

 ends of the femur or thigh-bone and tibia are each covered with 

 cartilage, and in contact, but neither of them is hollowed ; so that 

 the joint does not depend for its strength on its form, but on the 

 number and strength of its ligaments. Two of these are placed 

 externally and internally, as in all hinge-joints, and seven others 

 are arranged in different positions within and without it. The 

 kneepan (patella) is placed in front of it, and the whole is lined 

 with a synovial membrane, which is the largest in the body : hence 



