THE SKIN AND ITS APPENDAGES. 



273 



Muscular slips frequently encircle the lower part of the follicle, while 

 additional bands sometimes are given off to find attachment in the 

 fibrous sheath of the sweat-glands. 



THE SEBACEOUS GLANDS. 



These structures occur so closely connected with the hair- 

 follicles, into which they usually open, that the sebaceous glands 

 may be looked for wherever hairs exist ; in addition, the glands may 

 be present when hair-follicles are absent, as on the external genitalia 

 (labia minora, glans and prepuce of the penis), the eyelids (Mei- 

 bomian glands), and the red edge of the lips. The smallest se- 

 baceous glands are connected with the head-hairs, while the largest 

 are found on the mons Veneris, the labia 

 majora, and the scrotum. The size of these 

 structures is not proportionate to that of 

 the associated hairs, since frequently the fine 

 lanugo hairs possess large glands, a relation 

 also seen in the particularly well developed 

 sebaceous sacs connected with the fine hairs 

 on the nose and the face. The group of acini 

 is usually placed on the side towards which 

 the hairs slope, and occupies the interval be- 

 tween the hair-follicle and the arrector pili 

 muscle, the contractions of the latter aiding 

 in the expulsion of the secretion of the gland. 



The sebaceous glands are sometimes 

 simple but usually small compound saccular 

 structures possessing short ducts which 

 open into the hair-follicles near their upper 

 extremities. The periphery of the acini, 

 five to twenty in number, is lined by a pe- 

 ripheral layer of cuboidal epithelium, while 

 the greater part of the sacs is filled with 

 cells in various stages of fatty metamor- 

 phosis. 



The secretion of these glands, the sebum, 

 when fresh at the body-temperature, is a 



semi-fluid substance consisting of oil-droplets and the debris of 

 broken-down cells ; on exposure to the atmosphere it becomes of 

 the consistence of tallow. 



THE SWEAT-GLANDS. 



The sweat or sudoriparous glands are modified simple tubular 

 glands which extend from the free surface of the integument, where 



18 



Section of portion of seba- 

 ceous gland from human scalp, 

 including part of acinus : a, 

 membrana propria; b, periph- 

 eral layer of cuboidal cells ; c, 

 elements in which fatty meta- 

 morphosis is beginning ; tf, cells 

 filled with fatty particles and 

 exhibiting marked intra-cellular 

 net-works ; e, nuclei of cells. 



