REGION OF THE HIP. 499 



if this was not done it would be necessary to raise the limb by tilting the pelvis up 

 on that side. The left continues to advance flexed while the right gradually extends 

 (Fig. 499, .), and finally when the right is fully extended the left is likewise fully 

 extended (Fig. 499, f") and strikes the ground with the foot about at a right angle 

 to the leg. 



The object of flexion of all three joints is, first, to avoid shock in impact, and, 

 secondly, to raise the free foot and allow it to swing forward clear of the ground. 

 The object of extension is to push the body forward. 



Part Played by the Various Joints. The /)5>-joint flexes to an extent pro- 

 portionate to the length of the step (Fig. 499, A}. If this joint is put out of use by 

 being ankylosed, first, the shock of impact is more severe, no flexion being possible; 

 second, the limb can only be brought forward by bending the pelvis on the opposite 

 hip, and, to a certain extent, the trunk above backward; third, to aid still more to 

 advance the foot forward the pelvis will be rotated laterally on the opposite hip. 

 This causes a swaying of the trunk backward and forward and a side swing or 

 waddle of the pelvis. Fourth, the forward propulsive force is weakened by the loss 

 of the hip extensors. The knee, like the hip, lessens the shock of impact by flexing. 

 It raises the foot clear of the ground as it is swung forward, and it aids propulsion 

 by extension. If ankylosed, shock is increased, onward propulsive force is lost, and 



E. D. C. B. 



PIG. 499. Walking. Tracings from photographs by Muybridge. 



it is necessary to tilt the pelvis upward in order to raise the foot from the ground and 

 allow it to swing forward. This abducts one or both legs and causes marked wad- 

 dling. The ankle also reduces shock and gives propulsion ; if ankylosed, shock is 

 increased and propulsion weakened. This is the least necessary of the three joints 

 and to substitute it artificial appliances are useful, so that in quiet walking limp may 

 be almost lacking, but violent and complicated movements are to a large extent 

 impossible. The toes, especially the big toe, aid in propelling the body forward. 



REGION OF THE HIP. 



The hip is that portion of the body joining the lower extremity to the trunk. 

 It differs in construction from the shoulder, because it is designed for strength as 

 well as mobility; hence it is that the bones are heavier, stronger, with their proc- 

 esses more marked, and that the muscles also are bigger and more powerful. It is 

 often the seat of injury and disease, the bones being fractured, the joint luxated, 

 and frequently affected with tuberculosis and other diseases. 



BONES OF THE HIP. 



The bones of the hip are the innominate bone and femur. The innominate bone 

 has its shape determined by its relation to the trunk, being adapted to support and 

 protect the viscera, while the femur has its shape determined by its relation to the 

 extremity, being in the nature of a pole to support it. 



The innominate bone (Figs. 500 and 501) is composed of the ilium, ischium, 

 and pubis. These are united in the acetabulum by the triangular cartilage and 

 become ossified about the sixteenth year. The ilium has a crest which serves for 

 the attachment of the transverse abdominal muscles. At its anterior extremity is 



