488 



THE TISSUES. 



no hairs are present ; within which are (2) masses of cells. The 

 latter are arranged, first in a single, and rarely in a double layer, in 

 contact with the basement-membrane ; internally to which are other 

 cells containing more fat, arid which pass into the innermost of the 

 cells which are larger ( 7 J^ to -J 5 of an inch), and so filled with 

 colorless fat that they might be termed sebaceous cells. (Fig. 326.) 



A. One of the caeca of a common sebaceous gland ; a, epithelium sharply denned, but without any 

 basement-membrane, and passing continuously into the fat-cells, b (their contours drawn too indis- 

 tinctly), in the interior of the glandular tube. B. Sebaceous cells from A, and the cutaneous seba- 

 ceous matter ; a, smaller nucleated cells, still more of an epithelial character, and containing but 

 little fat ; 6, cells abounding in fat without visible nucleus ; c, cell in which the fat is beginning to 

 flow into one mass ; d, cell with one fat drop ; e, f, cell from which the fat has partially escaped. 

 Magnified 350 diameters. (Kolliker.) 



The fat in them sometimes appears in the form of a single drop 

 quite filling the cells; at others it still retains the form of distinct 

 small drops. In the former case, they resemble the adipose cells. 

 By endogenous development new cells are constantly produced in 

 the bottom of the glands, and thus the pre-existing cells are thrust 

 forward, and finally excreted through the neck of the gland upon 

 the cuticle. , 



It appears that no nerves are distributed to the sebaceous glands. 

 Nor are vessels distributed upon and between their lobules; while 

 numerous vessels and capillaries exist around the glands. 



These glands are developed from about the end of the fourth 

 month of embryonic life, together with the hairs, since they appear 

 as outgrowths or processes of the hair-sacs. Subsequently the pro- 

 cesses ^become filled with the cells above described ; and, finally, 

 they open on the surface, and the structure of the gland is now 

 complete. All the glands are at first simple, and most are so in the 

 foetus of seven months ; and the compound are formed by processes 

 proceeding from these. Sometimes a simple gland growing rapidly 



