604 DISSECTION OF THE THIGH. 



Dislocation may take place in both these lateral movements, the edge 

 of the cotyloid cavity serving as the fulcrum by which the femur can be 

 lifted out of the hollow ; in the one case (adduction) the neck of the femur 

 rests on the brim of the acetabulum, and in the other (abduction) the 

 great trochanter is supported on the margin of the joint-socket. After a 

 dislocation has been reduced, the state of adduction, with the knees 

 fastened together, is the securest position in which the limb can be placed, 

 inasmuch as the head of the femur then occupies the deepest part of the 

 acetabulum. 



In circumduction, the four kinds of angular motion above noticed take 

 place in succession, viz., flexion, abduction, extension, and adduction ; and 

 the limb describes a cone, whose base is at its extremity, and apex at the 

 union of the neck with the shaft of the femur. This movement is less 

 free than in the shoulder-joint, because of the greater bend between the 

 neck and shaft of the femur. 



There are two kinds of rotation, internal and external : in the former, 

 the great toe is turned in ; and in the latter, the more extensive of the 

 two, it is moved outwards. 



In rotation inwards, the head of the femur rolls backwards horizontally 

 across the acetabulum, the great trochanter being put forwards ; and the 

 shaft of the bone revolves around a line inside it, which passes from the 

 head to the inner condyle. During this movement the posterior half of 

 the capsule is put on the stretch, and the anterior is relaxed. 



In rotation out the head of the bone rolls forwards across the cotyloid 

 cavity, and the great trochanter is brought backwards, whilst the shaft of 

 the femur moves round the line on its inner side before noticed. The fore 

 part of the capsule is now put on the stretch, and the hinder is rendered 

 loose. 



The movement of rotation is destroyed by fracture of the neck of the 

 bone. Its degree is proportioned to the length of the neck, and is there- 

 fore greater in the femur than in the humerus. 



Use of bend of femur. By means of the angle at the union of the neck 

 with the shaft, the pelvis is more firmly propped than it would be if the 

 neck was in a line with the rest of the femur. It permits also greater 

 surface contact between the head of the femur and the hip bone, since the 

 whole heaii can be lodged in the cotyloid cavity in progression ; and gives 

 greater security to the joint in flexion and extension, for if the neck and 

 shaft of the bone were in a line, only half of the articular surface could 

 enter the socket of the innominate bone in walking, and running. The 

 important movement of rotation is also due to this angle ; and greater 

 space is obtained through it for the location of the adductor muscles on 

 the inner side of the femur. 



Dissection. After the limb is removed, the attachments of all the 

 muscles in the thigh are to ba examined more minutely before the dissec- 

 tion of the leg is undertaken. The muscles should not be removed from 

 the femur, but about two inches of each should be left for after study. 



