THE GLANDS OF THE SKIN. 



399 



in only a few regions of the body, as, for instance, in the glans penis 

 and foreskin (Tyson's glands), in the labia minora, angle of the 

 mouth, glandulae tarsales, and the Meibomian glands of the eyelids, 

 etc. As a rule the sebaceous gland empties by a wide excretory 

 duct into the upper third of the hair follicle. The walls of the duct 

 also produce secretion, and can therefore hardly be differentiated 

 from the rest of the gland. At its base the duct widens and is pro- 

 vided with a number of simple or branched alveoli. The sebaceous 

 glands are therefore of the type of simple branched alveolar glands, 

 varying in length from 0.2 mm. to 0.5 mm. They are surrounded 

 by connective-tissue sheaths, which at the same time cover the hair 

 follicles. Inside of the sheath is the membrana propria, which is a 

 continuation of the glassy membrane of the follicle. The two or 

 three basal strata of glandular cells must be regarded as a direct 

 continuation of the elements of the external root-sheath. In the 



Fig. 323. Section of alveoli from sebaceous gland of human scalp. 



more centrally placed strata the cells are distinctly changed in char- 

 acter ; their contents consist of fat globules, varying in size and 

 distributed throughout the protoplasm, giving this a reticular 

 appearance, while the nuclei suffer compression from the accumu- 

 lation of the fat globules and gradually become smaller and more 

 angular. Finally, the cells change directly into secretion, which is 

 then poured into the hair follicle as sebum. It is thus seen that in 

 the secretion of sebum the cells are consumed and must be re- 

 placed. This renewal takes place by the constant proliferation 

 of the basilar cells, which push the remains of the secreting cells 

 upward and finally take their places. The final disintegration of the 

 cells occurs either within the gland itself or between the hair follicle 



