A STUDY OF THE SKELETON 



179 



caps 



7. A STUDY OF JOINTS 



Definition of a Joint. Thus far we have considered the 

 bones of the skeleton as though they were independent of 

 each other. In the living 

 body, however, we know 

 that they are firmly attached 

 to one another, and that 

 thus a strong but movable 

 framework is formed. Any 

 region in the skeleton where 

 motion is possible between 

 two bones is catted a joint. 



Structure of a Leg Joint of 

 Lamb. 1 Certain tissues are 

 always present in a joint, 

 and most of them can be 

 easily seen in a leg joint of 

 lamb or veal. In the first 

 place, it is clear that in the 

 formation of a joint there 

 must be at least two sepa- FlQ 

 rate bones (compare with 

 Fig. 76). We find in the leg 

 joint which we are study- 

 ing that the bones are 

 bound tightly to one another 

 by tough bands of connec- 

 tive tissue called lig'a-ments 

 (Latin ligare = to bind), 

 and that motion is possible 

 in only two directions, like the movement of a door on 

 a hinge. When we studied the structure of a long bone, 

 we found a layer of cartilage covering the heads where- 

 ever any motion upon another bone took place, and on 



1 See "Laboratory Exercises," No. 35. 



fil- 



Section of 

 Kneejoint. 



cartilage on end of tibia, 

 connective tissue forming a 



capsule about joint. 

 e = tendon of extensor muscle. 

 fern = section of femur. 

 Jib = fibula. 

 I = ligaments between femur and 



tibia. 



pat = section of patella (kneecap). 

 tib = tibia in calf of leg. 



c 

 caps 



