GENERAL STRUCTURE OF THE BODY. 21 



motion or where there is great weight to be supported. 

 In a ball-and-socket joint, such as the hip, there is a 

 ligament in the form of a strong capsule which surrounds 

 the joint on all sides and limits its motion, while hinge 

 joints, like the elbow, and pivot joints, such as that 

 formed by the atlas on the axis, have lateral ligaments 

 that allow of freer motion. In the shoulder-joint, which 

 is the most freely movable joint in the body, the capsular 

 ligament is very lax. 



In general the kinds of motion possible in joints may 

 be said to be flexion, extension, abduction, adduction, 

 circumduction, and rotation. 



When much violence is applied to a joint and no dis- 

 location results, as in a sprain, there is often much 

 stretching and even laceration of the ligaments. 



Muscle. The flesh, which forms a large proportion of 

 the weight of the body, consists of muscular tissue. Of 

 this two kinds are found: 1. The striated or striped 

 muscle of animal life, which is under the control of the will 

 and so is known as voluntary muscle, and 2. the unstriped 

 or smooth muscle of organic life over which we have no 

 control, that is, the involuntary muscle. Each fiber of 

 striped muscle has an elastic, membranous sheath, the 

 sarcolemma, and consists of rod-shaped cells with a 

 nucleus along the edge, set end to end and having cross- 

 wise striations. In unstriated muscle the fibers, which 

 have no sarcolemma, consist of oval or spindle-shaped 

 cells, with a nucleus much smaller than that of striped 

 muscle and situated in the middle. In both kinds of 

 muscle the fibers are bound together with connective 

 tissue and blood-vessels into fasciculi or bundles, and 

 many bundles go to make up a muscle. The muscle in 

 turn has a connective tissue envelope or sheath, the 

 fascia. These fasciae are found throughout the body, the 

 superficial ones being just beneath the skin, while the 

 deep ones not only form sheaths for the various mus- 

 cles but form partitions between them and serve to 

 strengthen their attachments. The striped muscles are 



