HUMAN ANATOMY. 326 



which that end is attained : some being prevented from 

 changing their relative situations by certain modes of 

 articulation ; others, where only a slight motion is re- 

 quired, being united by cartilage ; and others, where 

 extensive and varied motions are wanted, as in the shoul- 

 der and hip joints, being connected by ligaments, mem- 

 branes, and muscles. 



Ligaments. Ligaments are white, fibrous, tough, 

 glistening, and flexible expansions, or cords, which occur 

 almost every where in the system, and, therefore, assum- 

 ing a great variety of forms and sizes. They are, for the 

 most part, exterior to the joints, and by their great 

 strength and small elasticity, preserve the relative posi- 

 tion or connection of the bones in their various move- 

 ments. 



Membranes. Membranes are thin, whitish webs, or 

 textures, more flexible and elastic than ligaments, and, 

 generally, of a more delicate fabric. They not only as- 

 sist in the security and motion of the joints, but fulfill a 

 variety of other offices. They surround, or line the cav- 

 ities and the organs of the system, and contribute to unite 

 and combine the whole ; and, at the same time, interpose 

 and preserve a distinction between separate parts, thus 

 enabling them to act independently of each other. They 

 vary in strength, texture, and color, and thus different 

 terms are applied to them in different parts of the body : 

 two within the skull are called maters ; as, pia and dura 

 mater : those which envelop muscular fibres are called 

 aponeurosis ; that which covers the lungs, and lines the 

 cavity of the chest, is termed the pleura; that which 

 lines the cavity of the abdomen, and its included viscera, 

 is called the peritoneum ; those which inclose the artic- 

 ulated surfaces are termed capsules ; while those cover- 

 ing the bones are the periosteum. In some other cases 

 the membranes are named tunics, or coats. 



By what different means are the hones united ? What are ligaments ? 

 What the uses of ligaments ? What are membranes ? Where are membranes 

 found ? What are those within the brain called ? What is an aponeurosis ? 

 What is the periosteum ? What is the peritoneum ? 



28 



