THE SKIX AXD ITS APPENDAGES. 



95 



from the accumulation of pent-up secretion. The largest sebaceous glands are 

 those found in the eyelids the Meibomian glands. 



The sudoriferous or sweat glands are the organs by which a large portion of 

 the aqueous and gaseous materials are excreted by the skin. They are found in 

 almost every part of this structure, and are situated in small pits in the deep parts 

 of the corium, or, more frequently, in the subcutaneous areolar tissue, surrounded 

 by a quantity of adipose tissue. They are small, lobular, reddish bodies, consist- 

 ing of a single convoluted tube, from which the efferent duct proceeds upward 

 through the corium and cuticle, becomes somewhat dilated at its extremity, and 

 opens on the surface of the cuticle by an oblique valve-like aperture. The efferent 

 duct, as it passes through the epidermis, presents a spiral arrangement, being 

 twisted like a corkscrew, in those parts where the epidermis is thick ; where, how- 

 ever, it is thin, the spiral arrangement does not exist. In the superficial layers 

 of the corium the duct is straight, but in the deeper layers it is convoluted or even 

 twisted. The spiral course of these ducts is especially distinct in the thick cuticle 

 of the palm of the hand and sole of the foot. The size of the glands varies. 

 They are especially large in those regions where the amount of perspiration is 

 great, as in the axilla?, where they form a thin, mammillated layer of a reddish 

 color, which corresponds exactly to the situation of the hair in this region ; they 

 are large also in the groin. Their number varies. They are most numerous on 

 the palm of the hand, presenting, according to Krause, 2800 orifices on a square 

 inch of the integument, and are rather less numerous on the sole of the foot. In 

 both of these situations the orifices of the ducts are exceedingly regular, and cor- 

 respond to the small transverse grooves which intersect the ridges of the papilla?. 

 In other situations they are more irregularly scattered, but in nearly equal num- 

 bers, over parts including the same extent of surface. In the neck and back they 

 are least numerous, their number amounting to 417 on the square inch (Krause). 

 Their total number is estimated by the same writer at 2.381.248. and, supposing 

 the aperture of each gland to represent a surface of Jg- of a line in diameter, he 

 calculates that the whole of these glands would present an evaporating surface of 

 about eight square inches. Each gland consists of a single tube intricately con- 

 voluted, terminating at one end by a blind extremity, and opening at the other 

 end upon the surface of the skin. In the larger glands this single duct usually 

 divides and subdivides dichotomously ; the smaller ducts ultimately terminating in 

 short ca?cal pouches, rarely anastomosing. The wall of the duct is thick, the 

 width of the canal rarely exceeding one-third of its diameter. The tube, both in 

 the gland and where it forms the excre- 

 tory duct, consists of two layers an 

 outer, formed by fine areolar tissue, and 

 an inner layer of epithelium. The 

 external or fibro-cellular coat is thin, 

 continuous with the superficial layer of 

 the corium. and extends only as high 

 as the surface of the true skin. The 

 epithelial lining in the distal part of the 

 coiled tube of the gland proper consists 

 of a single layer of cubical epithelium, 

 supported on a basement membrane, and 

 beneath it. between the epithelium and 

 the fibro-cellular coat, there is a layer of 

 what are usually regarded as plain mus- 

 cular fibres, arranged longitudinally. In 

 the duct and the proximal part of the 

 coiled tube of the gland proper there 

 are two or more layers of polyhedral 

 cells, lined on their internal surface L e. next the lumen of the tube by a deli- 

 cate membrane or cuticle, and on their outer surface by a limiting membrana 



FIG. 70. Coiled tube of a sweat-gland cut in vari- 

 ous directions, a. Longitudinal section of the proxi- 

 mal part of the coiled tube. b. Transverse section of 

 the same. c. Longitudinal section of the distal part of 

 the coiled tube. d. Transverse section of the same. 

 (From Klein and Noble Smith's AUas of Histology.) 



