ELASTIC TISSUE. 



77 



tissue held together by a small amount of intervening fibrous tissue. In transverse 

 section of such ligaments (Pig. 104), the individual elastic fibres appear as minute 

 polygonal areas separated by the fibrous fibrillae and the associated connective-tissue 

 cells. Within the walls of the large blood-vessels the elastic tissue is arranged as 



membranous expansions containing numerous 

 p,G J02. openings of varying size : XhesQ fenestrated mem- 



branes, as they are called, are probably formed 

 i; by the junction and fusion of broad ribbon-like 



Ic^ elastic fibres. Elastic tissue yields elastin upon 



Fig. 103. 



Reticular connective tissue from lymph- 

 node. X 350. The cells lie upon the fibrous 

 tissue at the points of intersection. 



Portions of isolated elastic fibres from ligamen- 

 turn nuchse of ox. X 375. 



boiling in water, and disappears upon being subjected to pancreatic digestion, thus 

 differing from fibrous and reticular tissue ; by taking advantage of the especial affinity 

 that elastic tissue possesses for certain stains, as orcein, a much wider and more 

 generous distribution of elastic tissue has been established than was formerly appre- 

 ciated. 



The development of elastic tissue has shared the uncertainty surrounding 

 the mode of production of fibrous tissue, since here, as there, two opposed views 

 have been held, — one of a cellular and 



one of an independent origin. Accord- ^'^- ^°4- 



ing to the view of an independent origin, 

 the older one, the elastic fibres first 

 appear as rows of minute beads in the 

 intercellular matrix. These linearly dis- 

 posed beads gradually fuse, thus produc- 

 ing the primary elastic fibres. According 

 to the view of an intracellular origin, 

 the one less generally accepted, the 

 elastic fibres are derived directly from 

 the exoplasm of the young connective 

 tissue cells, as in the case of the white 

 fibrils. 



The density of connective substances 

 depends upon the amount and arrange- 

 ment of the fibrous tissue ; the extensibility 

 is determined by the proportion of elastic 

 tissue present. When the former occurs 

 in well-defined bundles, felted together 



into interlacing lamellae, dense and resistant structures result, as fasciae, the cornea, 

 etc. ; in such structures the cement- or ground-substance within the interfascic- 

 ular clefts usually contains the lymph-spaces occupied by the connective-tissue 

 cells. 



Tendon. — Tendon consists of dense connective tissue composed almost en- 

 tirely of white fibrous tissue arranged in parallel bundles. The individual fibrillae 



Elastic fibres 

 in section 



Interfibrillar 

 connective tissue 



Nucleus of con 

 nective-tissue 

 cell 



Transverse section of ligamentum nucha" of o.x. X 45°- 



