MUSCULAR AND SKELETAL SYSTEMS. 



225 



All of these characters, intended for easy motion and 

 to prevent dislocation, are common to all movable joints; 

 but to these in the case of 

 hinge joints are added (e) 

 two strong ligaments, one 

 on each side, which hold 



Fig. 143. — Diagrammatic view of 

 the knee joint. The dotted lines 

 show the position of the capsule 

 and of the lateral ligaments ; the 

 black lines show the crossed liga- 

 ments. 



Fig. 144. — Section through the hip 

 joint, showing the capsule (cl) 

 and the round ligament (rl )„ 



the parts together and yet allow free motion in one 

 plane. These are the lateral ligaments. They are found 

 in all hinge joints. In addition to these (/), in the 

 knee joint there are two crossed ligaments within the 

 joint itself, as shown in Fig. 143. 



In ball-and-socket joints we have, of course, a, b, c, d ; 

 but in the case of the hip joint, in addition to these, 

 there is a short, strong, round ligament running from 

 the bottom of the deep socket to the top of the ball, as 

 shown in the diagram (Fig. 144). 



SOME EXAMPLES OF ADAPTATION. 



The articulated skeleton together forms a really 

 wonderful contrivance. Some examples of adaptation 

 may be mentioned. I select such as lead to interesting 

 comparisons with other vertebrates. 



