4 2 



HISTOLOGY. 



which are highly refractive, that is, they so. reflect light as to change from 

 bright to very dark objects on varying the focus. They may be extremely 

 fine, or quite broad, but the latter are not divisible into smaller elements 



or fibrils. Seen in specimens which have 

 not been torn apart, the elastic fibers form a 

 network, Fig. 42, A, and the smooth manner 

 in which they fuse at its angles is charac- 

 teristic. When the net is broken the fibers 

 retract in irregular spirals. The elastic 

 fibers are thought to be of exoplasmic origin, 

 as is suggested by Fig. 42, B. Elastic sub- 

 stance may appear within the cell as fila- 

 ments, or as granules which later fuse. In 

 some cases the fibers forming the elastic net 

 are wider than its apertures, as shown in 

 the lower part of Fig. 43, A. Here they 

 constitute a perforated elastic plate, called a 

 fenestrated membrane, and such occur in 

 many blood vessels. B and C of the same figure present elastic elements 

 from the ligamentum nuchae, a structure containing relatively little white 



FIG. 42. 



A, Elastic fibers of the subcutaneous 

 areolar tissue of a rabbit. (After 

 Schafer.) B, Cells in relation 

 with elastic fibers, after treatment 

 with acetic acid. Subcutaneous 

 tissue of a fetal pig. (After Mall.) 



FIG 43. ELASTIC FIBERS. 



A, Network of thick fibers below, passing into a fenestrated membrane above. (From the endoacrdium 

 of man.) B, Thick elastic fibers, f, from the ligamentum nuchae of the ox; b, white fibers. C, 

 Cross section of the ligamentum nuchae, lettered as in B. 



fiber, and hence used for the chemical analysis of elastic fiber. The 

 stylo-hyoid ligament and the ligamentaflava are also elastic ligaments. 



Elastic fibers are not destroyed by dilute acids (Fig. 41, B) or alkalies. 

 They consist of elastin, an albuminoid body which does not yield gelatin 



