120 



ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



perfect form of Muscular Fibre, the secondary deposit has only a granular or 

 amorphous character ; but in the striated Muscular fibre, it is composed of 

 minute cells. 



As it is not requisite here to say anything further of simple Elementary 

 Membrane, we shall at once pass on to the second group of Tissues ; one of 

 great extent and importance in the bodies of all the higher Animals. 



4. Of the Simple Fibrous Tissues. 



138. A very large proportion of the body, in the higher Animals, is com- 

 posed of a tissue, to which the name of "Cellular" was formerly given. This 

 term, however, is so much more applicable to those structures, which are 

 composed of a congeries of distinct Cells, and the use of it for both purposes 

 is likely to engender so much confusion, that it is to be wished that its appli- 

 cation to this purpose should be altogether discontinued. The tissue in ques- 

 tion, now generally designated the Areolar, is found, when examined under 

 the Microscope, to consist of a network of minute fibres and bands, inter- 

 woven in every direction, so as to leave innumerable interstices, which com- 

 municate with each other. The two kinds 



Fig- 22. of Fibrous tissue, which elsewhere exist se- 



parately, the white, and the yellow, may 

 be detected in Areolar tissue ; as was first 

 pointed out by Messrs. Todd and Bowman. 

 The White presents itself in the form of 

 inelastic bands of variable size, the largest 

 1 -500th of an inch in breadth, somewhat 

 wavy in their direction, and marked longitu- 

 dinally by numerous streaks (Fig. 23); these 

 streaks are rather the indications of a longi- 

 tudinal creasing, than a true separation into 

 component fibres; for it is impossible by any 

 art to tear up the band into filaments of a de- 

 terminate size, although it manifests a decided 

 tendency to tear lengthways. Sometimes, 

 however, distinct fibres may be traced, whose diameter varies from about 

 l-15,000th to l-20,000th of an inch. The Yellow fibrous element exists in 

 the form of long, single, elastic, branched filaments, with a dark decided bor- 

 der, and disposed to curl when not put on the stretch (Fig. 24). These inter- 

 lace with the others, but appear to have no continuity of substance with them. 

 They are for the most part between l-5000th and 1-10,000 of an inch in 

 thickness ; but they are often met with both larger and smaller. The pro- 

 portion of this element varies greatly in different parts; being greatest in those 

 situations, in which the greatest elasticity is required. Sometimes we find 

 elastic fibres passing round the fasciculi of the white tissue, constricting them 

 with distinct rings, or with a continuous spiral ; such are termed by Ilcnle 

 nucleus-filaments, from his idea of their origin ( 133). This remarkable 

 disposition of the yellow fibres is best seen in the areolar tissue, that accom- 

 panies the arteries at the base of the brain. The effect of Acetic acid upon 

 these two elements is very different ; the while immediately swells up, and 

 becomes transparent; whilst the yellow remains unchanged. This agent fre- 

 quently brings into view certain oval corpuscles, which lie in the midst of 

 the bands and threads, and which sometimes appear to have delicate prolonga- 

 tions among them. These are usually supposed to be the persistent nuclei 

 of the cells, from which the tissue was developed ; but, as already pointed 

 out, it is doubtful whether the fibres of this tissue are ever formed by the me- 



Arrangement of Fibres in Areolar Tissue- 

 Magnified 135 diameters. 



