106 THE MECHANICAL FUNCTIONS. 



stance, with the membranes surrounding the 

 brain of quadrupeds, and which form two par- 

 titions, the one vertical, the other horizontal ; 

 both being firmly stretched in their respective 

 positions, and serving to divide the pressure. In 

 other cases these sheets of fibrous membrane 

 are employed as bandages, tightly bracing the 

 muscles, and retaining them in their relative 

 situations. The joints are surrounded by similar 

 bandages, known by the name of Capsular Li- 

 gaments. 



o 



In following the series of animal structures in 

 the order of their increasing density, we find the 

 proportion of albumen which enters into their 

 composition becoming greater, while that of the 

 gelatin and mucilage diminishes. When the 

 product is more uniform in its composition it is 

 in general less elastic than when it consists of a 

 more complex combination of ingredients. A 

 great preponderance of albumen tends also to 

 diminish the elasticity. Thus the densest kinds 

 of fibrous texture present, instead of thin and 

 broad expansions of elastic membrane, the thick 

 and elongated form of inextensible cords, con- 

 stituting the ordinary Ligaments, and the Ten- 

 dons. These structures resist with great power 

 any force calculated to extend them : a property 

 which of course excludes elasticity, but, when 

 united with flexibility, implies great toughness. 

 In a word, they possess all the qualities that can 



