THE CONNECTIVE TISSUES AND THE SKELETAL SYSTEM. 171 



parent cells and lie free in the "ground substance" (Figs. 145, 146). This 

 applies to both fibrillated and elastic fibers and the same cell may produce 

 both kinds of fibers, i. e., the same cell that produces fibrillated ("white") fibers 

 may also produce elastic ("yellow") fibers. The fibers, although not derived 

 primarily from the "ground substance," probably do increase in size by intus- 

 susceptive growth. Thus the "ground substance," while probably not capable 

 of producing fibers, is an active factor in their further growth. 



FIG. 147. Longitudinal section of developing ligament from finger of 

 human foetus of 6 months. Photograph. 



In any type of connective tissue where the fibers form the most characteristic 

 feature, such as the looser forms (areolar, reticular) or such as the-denser forms 

 (fascia, tendons, ligaments), the structure depends 'upon the secondary ar- 

 rangement of the fibers and not upon any peculiarity of origin. In areolar 

 tissue, for example, the fibers are derived from the cells, as described above, and 

 become so arranged as to look haphazard. In fascia, tendons and ligaments 

 the fibers arise in the same manner but come to lie parallel, with the cells en- 

 closed among them in more or less distinct rows (Fig. 147). 



Adipose Tissue. Adipose tissue is a form of connective tissue in which 

 the fatty element replaces to a great extent the cytoplasm in many of the 

 embryonic connective tissue cells. It always develops in close relation to blood 



