OF THE GLANDS OF THE SKIN. 



219 



selves ami incline obliquely towards the bottom of the sac, pyriform 

 and flask-shaped. A formation of fat in the internal cells now com- 

 mences (Fig. 88, A), which, beginning at the bottom of the pyriform pro- 

 cesses, is continued, also, into their pedicles, and finally includes the 

 cells of the outer root-sheath, until at last the fat cells reach as far as 

 the canal of the hair-sac (Fig. 88, B). The gland and its contents are 



Fig. 88. 



now complete, and it needs only that the cells at the bottom of the 

 gland, or the glandular vesicles, should multiply, to force the sebaceous 

 cells in the duct into the hair-sac, and fully to establish the secretion. 

 The sebaceous glands, therefore, like the sudoriparous, are, at first, 

 solid outgrowths of the Malpighian layer of the skin, for which an ex- 

 ternal opening is not developed till afterwards, and the first cutaneous 

 sebaceous matter is formed by a metamorphosis of the inner cells of the 

 rudiment of the gland, while the space which these cells occupied be- 

 comes the cavity of the gland, which, however, never appears empty, 

 but is continually filled by successive generations of cells. 



The development of the glands, up to this point, proceeds pretty 

 quickly. It may be stated generally, that so long as the hairs have not 

 appeared externally, the rudiments of the glands are papillary, measure 

 scarcely more than 0-03 of a line, and for the most part contain cells 

 which are still quite pale ; after the hairs have made their appearance 

 externally, we find larger pyriform rudiments with a thicker end, of 

 0-024-0-05 of a line, the cells of which are partly still pale, partly 



Fig. SS. — To elucidate tlie development of the sebaceous glands in a six-months' fcetus : 

 a, hair; b, inner root-sheatli, here more closely resembling the horny layer of the epidermis; 

 c, outer root-sheath ; rf, rudiments of the sebaceous glands. ^, flask-shaped rudiment of the 

 gland, with fat developed in the central cells; J5, larger rudiments; the development of fat 

 has taken place also in their neck, and fatty cells have been excreted into the hair-sac, 

 giving rise to the glandular cavity and the secretion. — Magnified about 250 diameters. 



