SWEAT-GLANDS. 



427 



minora, and, in some individuals, at the red margin of the lips, near the angle of the 

 mouth), they open into the hair-follicles, and are found wherever there are hairs. 

 Each has a short duct, which opens at a little distance within the mouth of the 

 hair-follicle, and by its other end, leads to a cluster of small rounded secreting 

 saecules, which as well as the duct are lined by epithelium (fig. 489), usually 

 charged with the fatty secretion. The cells as they multiply and become filled with 

 the fatty granules advance to the lumen of the alveoli. Here they become 

 disintegrated, and the fatty and other matters with which they are charged form 

 the secretion of the gland, which is dis- 

 charged by the duct into the mouth of 

 the hair-follicle. The 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 sub- 

 stance of the corium. They are usually placed 

 on the side to which the hair slopes, and in the 

 angle formed by the junction of the arrector 

 pili with the hair, so that when the muscular 

 fibres contract they tend to compress the 

 gland. Several may open into the same hair- 

 follicle, 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 alas of the nose and other parts 

 of the face, and there they often become 

 unduly charged with pent-up secretion. 



The Meibomian glands of the eyelids are 

 regarded as modified sebaceous glands. 



Development of the sebaceous glands. 

 The rudiments of the sebaceous glands 

 sprout like little buds from the sides of the 

 hair-follicles ; they are at first, in fact, excre- 

 scences of the external root-sheath (fig. .486, s), 

 and are composed entirely of similar cells. 

 Each little process soon assumes a flask-shape 



and the central cells become occupied by fat particles. This fatty transformation 

 of the cells extends itself along the axis of the pedicle until it penetrates through 

 the root-sheath, and the fat-cells thus escape into the cavity of the hair-follicle, and 

 constitute the first secretion of the sebaceous gland. They are soon succeeded by 

 others of the same kind, and the little gland is established in its office. Additional 

 saccules and recesses, by which the originally simple cavity of the gland is complicated, 

 are formed by budding out of its epithelium, as the first was produced from the 

 epithelial root-sheath, and are excavated in a similar manner. 



The sudoriferous glands or sweat-glands (figs. 471 and 490). These are 

 seated on the under-surface of the corium, and at variable depths in the subcu- 

 taneous adipose tissue. To the naked eye they have the appearance of small round 

 reddish bodies, each of which, when examined with the microscope, is found to 

 consist of a tube, coiled up into a ball (though sometimes forming an irregular or 

 flattened figure) ; from which the tube is continued, as the duct of the gland, 

 upwards through the true skin and cuticle, and opens on the surface by a slightly 

 widened orifice. The secreting tube is considerably larger than the duct, and also 



Fig. 489. LONGITUDINAL'SECTION OF A SEBA- 

 CEOUS GLAND FROM THE CHEEK WITH A 

 SMAT.L HAIR GROWING THROUGH ITS 



DUCT. HUMAN. (Toldt.) 



VOL. I. 



p p 



