SEBACEOUS GLANDS. 



229 



Fiff. 158. 



geneous limiting membrane, which is prolonged above between the cerium 

 and cuticle. The subsequent changes consist in the elongation of the radimentary 

 gland, the formation of a cavity along its 

 axis — -at fii'st without an outlet — the prolonga- 

 tion of its canal through the epidermis to open 

 on the surface, and, in the meantime, the coil- 

 ing up of the gradually lengthening gland-tube 

 into a compact ball, and the twisting of the 

 excretory duct as it proceeds to the orifice. The 

 original homogeneous membrane of the duct 

 becomes thickened and is continuous with the 

 surface of the corium, whilst an epithelium 

 appears within, consisting of several layers of 

 polyhedral or rounded cells. 



The ceniminous glands in the auditory 

 passage consist of a tube coiled into a 

 baU, like the sweat-glands ; and KoUiker's 

 investigations show such a further corre- 

 spondence between the two, in structui-e and 

 mode of develoi^ment as to lead him to regard 

 the ceruminous glands as a mere local variety 

 of the sudoriferous, which present specialities 

 both of structui-e and secretion in particular 

 regions of the body. 



The sebaceous glands (fig. 158) 

 pour out their secretion at the roots 

 of the hairs, for, with very few excep- 

 tions, they open into the hair-follicles, 

 and are found wherever there are hairs. 

 Each has a small duct, which opens at 

 a short distance within the mouth of 

 the hair-follicle, and by its other end, 

 leads to a cluster of small rounded 

 secreting saccules, which as well as the 

 duct are lined by epithelium, and 

 usually charged with the fatty secretion, 

 mixed with detached epithelium-par- 

 ticles. Tiie number of saccular recesses 

 connected with the duct usually varies 

 from four or five to twenty ; it may 

 be reduced to two or three, in very 

 small glands, or even to one, but this 

 is rare. These glands are lodged in the 

 substance of the corium. Several may 



open into the same hair-follicle, surrounding it on all sides, and their 

 size is not regulated by the magnitude of the hair. Thus, some of the 

 largest are connected with the fine downy hairs on the alte of the nose 

 and other parts of the face, and there they often become unduly charged 

 with pent-up secretion. 



Fig. 158. — Sebaceous Gland froh 

 THE Face vhth branched duct, 



OPENING INTO A HaIR-FoLLICLE, 

 MAGNIFIED 50 DIAMETERS (frOm 



Kijlliker). 



a, epithelium continuous with 

 h, the mucous laj'cr of epidermis ; 

 c, contents of gland; d, d, the 

 groups of saccules on the branches 

 of the duct ; e, hair-follicle ; /, 

 hair. 



Development of the sebaceous glands.— The nidiments of the sebaceous 

 glands sprout like little buds from the sides of the hair-follicles ; they are at first, 

 in fact, excrescences of the external or mucous layer of the root-sheath (fig. 159), 

 and are composed entirely of nucleated cells. Each little process soon assumes 

 a flask shape and is at fii-st solid ; but in due time a group of cells containing 

 fat particles appears in its centre, and gradually extends itself along the 



