1040 



VERTEBHATED ANIMALS 



removed is commonly designated as cartilage, this is shown by 

 careful microscopic analysis not to be a correct description of it, 

 since it does not show any of the characteristic structure of car- 

 tilage, but is capable of being torn into lamella?, in which, if suf- 

 ficiently thin, the ordinary structure of a fibrous membrane can be 

 distinguished. The yellow fibrous tissue exists in the form of long, 

 single, elastic, branching filaments, with a dark decided border ; 

 which are disposed to curl when not put on the stretch (fig. 774), 

 and frequently anastomose, so as to form a network. They are for 

 the most part between -uVoth and nroinft'h of an inch in diameter; 

 but they are often met with both larger and smaller. This tissue 

 does not undergo any change when treated with acetic- acid. It 

 exists alone (that is, without any mixture of the white) in parts 

 which require a peculiar elasticity, such as the middle coat of the 

 arteries, the 'vocal cords,' the ' ligameiitum nuchai' of quadrupeds, 



the elastic ligament which 

 holds together the valves of 

 a bivalve shell, and that by 

 which the claws of the feline 

 tribe are retracted when 

 not in use ; and it enters 

 largely into the composition 

 of areolar or connective 

 tissue, 



The tissue formerly 

 known to anatomists as 

 cellular,' but now more 

 properly designated connec- 

 tive or areolar tissue, con- 

 sists of a network of minute 

 fibres and bands which are 



interwoven in every direction, so as to leave innumerable areohc or 

 little spaces that communicate freely with one another. Of these 

 fibres some are of the ' yellow ' or elastic kind, but the majority are 

 composed of the ' white ' fibrous tissue ; and. as in that form of ele- 

 mentary structure, they frequently present the condition of broad 

 flattened bands or membranous shreds in which no distinct fibrous 

 arrangement is visible. The proportion of the t\vo forms varies, 

 according to the amount of elasticity, or of simple resisting power, 

 which the endowments of the part may require. We find this tissue 

 in a very large proportion of the bodies of higher animals; thus it 

 binds together the ultimate muscular fibres into minute fasciculi, 

 unites these fasciculi into larger ones, these again into still larger 

 ones which are obvious to the eye, and these into the entire muscle; 

 whilst it also forms the membranous divisions between distinct 

 muscles. In like manner it unites the elements of nerves, glands. 

 A-c.. binds together the fat cells into minute masses (tig. 7SD). these 

 into large ones, ami so on: and in this way penetrates and forms 

 part of all the softer organs of the body. But whilst the fibrous 

 structures of which the formed tissue' is composed have a purely 

 mechanical fund ion. there is good reason to regard the -connective 



FIG. 774. Yellow fibrous tissue from liga- 

 mentum nuchre of calf. 



