VERTEBRATED ANIMALS. 



273 



fibrous tissue exists in the form of long, single, elastic, branching fila- 

 ments with a dark decided border; which are disposed to curl when not 

 put on the stretch (Fig. 462), and frequently anastomose, so as to form 

 a network. They are for the most part between l-5000th and 1-10, 000th 

 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 

 arteries, the * vocal cords/ 'ligamentumnuchae' of Quadrupeds, the elas- 

 tic 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 tis- 



sue. 



669. The tissue formerly known to Anatomists as 'cellular,' but now 

 more properly designated connective or areolar tissue, consists of a net- 



FIG. 461. 



FIG. 462. 



Portion of young Tendon, show- 

 ing the corpuscles of Germinal Mat- 

 ter, with their stellate prolongations, 

 interposed among its fibres. 



Yellow Fibrous Tissue from Ligamentum 

 Nuchae of Calf. 



work of minute fibres and bands, which are interwoven in every direction, 

 so as to leave innumerable areolce or little spaces that communicate freely 

 with one another. Of these fibres, some are of the * yellow 7 or elastic 

 kind, but the majority are composed of the * white'' fibrous tissue; and, 

 as in that form of elementary structure, they frequently present the con- 

 dition of broad flattened bands or membranous shreds in which no dis- 

 tinct fibrous arrangement is visible. The proportion of the two 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 to- 

 gether 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, etc., binds together the fat-cells 

 into minute masses (Fig. 468), these into large ones, and so on; and in this 

 18 



