THE CONNECTIVE TISSUES AND THE SKELETAL SYSTEM. 



167 



substance in bundles (fibers). These fibrillated fibers are collaginous in 

 character. Elastic fibers, while not fibrillated, probably have a similar 

 origin. This first step in development gives rise to a loose, delicate tissue 

 in the embryo, known as embryonal connective tissue, from which all the 

 adult forms, except reticular tissue, develop. 



The areolar tissue of the adult retains many of the general characters of 

 embryonal connective tissue. The fibers, both collaginous and elastic, are 

 loosely arranged and extend in all directions. The cells (fibroblasts) are 

 fewer, however, and while they are characterized by irregular, branching 

 forms it is not known whether their processes anastomose. 



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

 human foetus of 6 months. Photograph. 



In any fibrous tissue, such as areolar, or the denser forms (fascia, tendons, 

 ligaments), the structure depends upon the secondary arrangement of the 

 fibers and not upon any peculiarity of origin. In all these forms the fibers 

 have the same origin, but in the denser fascia, tendons and ligaments they 

 become arranged in parallel lines (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 



