ELASTIC TISSUE. 



37 



Adipose tissue is widely distributed through the body ; indeed, 

 it is an exception to find areolar tissue without some fat 

 in its areolae. The principal exceptions are the areolar tissue 

 beneath the skin of the eyelids, the penis, the scrotum, and 

 the labia minora. There is also no adipose tissue within the 

 cranium, in the liver, or in the lung, except near its root. It 

 is to be understood that this statement does not apply to fat, but 

 to adipose tissue, which is characterized by the fact that the fat 

 is enclosed in a protoplasmic envelope. The fat is formed from 

 the protoplasmic connective-tissue corpuscles, the cell-wall of 

 which forms the wall of the vesicle. The nucleus of the cell 

 remains, although it is not always readily discernible. 



Retiform Tissue (Fig. 28). This may be defined as areolar 

 tissue whose ground-substance is fluid, and in which but few, if 

 any, elastic fibers exist, and the white fibers form a close network. 

 Authorities differ as to the identity of the white fibers of areolar 

 and those of retiform tissue ; some claim that their different be- 

 havior to certain reagents demonstrates them not to be the same. 

 Retiform tissue exists in mucous membranes. 



I/ymphoid Tissue. When the areolae of retiform tissue 

 contain lymph-corpuscles, which will be described in connection 

 with the blood, the tis- 

 sue is lymphoid or ade- 

 noid. It is found in lym- 

 phatic glands, the thy- 

 mus gland, the tonsils, 

 solitary glands, patches 

 of Peyer, and Malpigh- 

 ian corpuscles of the 

 spleen. 



Elastic Tissue 

 (Fig. 25). This tissue 

 is composed of fibers or 

 membranes which are 

 characterized by their 

 elasticity and a yellow 

 color. By elasticity is 

 defined "that property 

 of matter by virtue of 

 which a body tends to 

 return to a former or 

 normal size, shape, or 

 attitude, after being de- 

 flected or disturbed." The tissue exists in the ligamenta subflava 

 of the vertebrae, the vocal cords, between the cartilages of the 

 larynx, in the longitudinal coat of the bronchi, the lungs, the 

 middle coat of the larger arteries (such as the aorta and caro- 



Tendon-cell. 



Tendon-fibers. 



FIG. 29. Longitudinal section of tendon ; X 270 

 (Bohm and Davidoff). 



