FIBROUS MEMBRANES AND LIGAMENTS. 41 



strain has to be borne. This is the case with the Ligaments, 

 which bind together the bones at the joints, the Tendons, by 

 which the muscles are usually attached to the bones, and the 

 tough Fibrous Membranes that envelope and protect many 

 of the most important viscera. In these any considerable 

 amount of elasticity would be misplaced ; and we conse- 

 quently find that they are chiefly or entirely composed of the 

 white fibrous tissue. Whenever an elastic ligament is re- 

 quired, however, we find the white replaced by yellow. One 

 of the best examples of this is seen in the ligament of the 

 neck of many quadrupeds, commonly known as the paxy- 

 waxy ; which is given to the large herbivorous quadrupecls, 

 such as the ox, to assist them in supporting their heavy 

 heads with as little exertion as possible ; whilst carnivorous 

 quadrupeds, such as the lion and tiger, are endowed with it 

 to give them additional power of carrying away heavy bur- 

 dens in their mouths. In Man we scarcely find a trace of 

 it. This yellow fibrous tissue is found, moreover, in the walls 

 of the arteries ( 248), to which it gives their peculiar elas- 

 ticity; and it also forms the vocal cords of the larynx ( 681). 

 It is by the same kind of elastic ligament that the claws of 

 the Feline tribe are drawn back into their sheaths when not 

 in use, being projected (when required) 'by muscular action ; 

 and that the two pieces of the shell of Bivalve Mollusks are 

 united at the hinge, and are at the same time kept apart for 

 the admission of water between them, except when the 

 animal forcibly draws them together by its adductor muscle 

 ( 113). 



30. All these fibrous tissues, then, are concerned in actions 

 purely mechanical; and there is nothing in their properties 

 which is so distinct from those of inorganic substances, as to 

 require to be considered as vital. We may consider them, 

 therefore, as among the lowest forms of animal tissue ; and 

 accordingly we find that, when the higher forms degenerate 

 or waste away, these appear in their place. Such a degene- 

 ration may take place simply from want of use. Thus if, 

 from palsy or want of power of the nerves, the muscles of 

 the legs are disused for several years, they will lose their 

 peculiar property of contractility ( 5) ; and it will be found 

 that scarcely any true muscular structure remains, but that it 

 is replaced by some form of fibrous tissue. Or again, if the 



