FORMATION OF SEBACEOUS MATTER. 



375 



FIG. 111. 



of which we have set up the secretion of milk and seba- 

 ceous matter as the true types. That these two secre- 

 tions are analogous to one another, is simply explained 

 by the circumstance that the mammary gland is really 

 nothing more than an enormously developed and pecu- 

 liarly formed accumulation of cutaneous (sebaceous) 

 glands. In their development both classes are perfectly 

 analogous. Both are produced, by means of a progres- 

 sive proliferation, from the internal layers of the epider- 

 mis (p. 68, Fig. 18, A). To the same category also be- 

 long the ceruminous glands of the ear, and the large 

 glands of the axilla. In all these 

 cases the fat, which constitutes the 

 chief constituent of milk, at least as 

 far as its external appearance is 

 concerned, and which furnishes the 

 sebaceous secretion, originates in 

 the interior of epithelial cells 

 which gradually perish and set the 

 fat free, whilst scarcely a trace of 

 the cells is preserved. The se- 

 baceous glands are generally seated 

 on the sides of the hair-follicles 

 at some depth below the surface ; 

 we there find a series of mi- 

 nute lobules, into which a prolon- 

 gation of the rete mucosum is un- 

 interruptedly continued. The cells 

 of this become more numerous and 

 larger, so as to fill the gland-sacs 

 with a nearly solid matter. Then the fat begins to be 



Fig. 111. Hair-follicle with sebaceous glands from the skin. c. The hair, b its 

 bulb, e, e, the layers of cells dipping down from the epidermis into the hair-follicle. 

 g g. Sebaceous glands in the act of secreting sebaceous matter ; at /, the secretion 

 mounting up by the side of the hair and accumulating. 280 diameters. 



