84 GENERAL ANATOMY. 



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 the skin, and are situated in small pits in the deep parts 

 of the corium, or in the subcutaneous areolar tissue, surrounded by a quantity 

 of adipose tissue. They are small, lobular, reddish bodies, consisting of one 

 or more convoluted tubuli, from which the efferent duct proceeds upwards 

 through the corium and cuticle, and opens upon the surface by a slightly en- 

 larged orifice. The efferent duct, as it passes through the corium, pursues, for 

 a short distance, a spiral course, becoming straight in the more superficial part 

 of this layer, and opens on the surface of the cuticle by an oblique valve-like 

 aperture. In the parts where the epidermis is thin, the ducts are finer and al- 

 most straight in their course; but where the epidermis is thicker, they assume 

 again a spiral arrangement, the separate windings of the tube being as close and 

 as regular as those of a common screw. 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 these glands varies. They are especially large in those 

 regions where the amount of perspiration is great, as in the axillae, 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, pre- 

 senting, 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 situa- 

 tions, the orifices of the ducts are exceedingly regular, and correspond to the 

 small transverse grooves which intersect the ridges of papillae. In other situations 

 they are more irregularly scattered, but in nearly equal numbers over parts in- 

 cluding the same extent of surface. In the neck and back they are least nume- 

 rous, 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 $ 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 convoluted, 

 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 csecal 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 excretory 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 is much thicker, continuous with the epidermis, and alone forms 

 the spiral portion of the tube. When the cuticle is carefully removed from the 

 surface of the cutis, these convoluted tubes of epidermis may be drawn out, and 

 form nipple-shaped projections on its under surface. According to Kolliker, a 

 layer of non-striated muscular fibres, arranged longitudinally, is found between 

 the areolar and epithelial coats of the ducts of the larger sweat-glands, as in the 

 axilla, root of the penis, on the labia majora, and round the anus. 



The contents of the smaller sweat-glands are quite fluid; but in the larger 

 glands, the contents are semi-fluid and opaque, and contain a number of col- 

 ored granules, and cells which appear analogous to epithelial cells. 



