THE SKIN AND ITS APPENDAGES. 



275 



FIG. 310. 



are eccentrically placed, while the border of the cells next the lumen 

 presents a thickened edge sometimes described as a cuticle. 



Immediately outside the epithelial cells, between these and the 

 basement-membrane, lies a thin 

 layer of involuntary muscle ; 

 this tissue occurs only in the se- 

 cretory division of the tube, and 

 is best developed in the larger 

 glands, where the muscle -cells 

 form a complete layer. The in- 

 dividual convolutions of the 

 tube constituting the coil are held 

 together by delicate connective 

 tissue, which additionally furnishes 

 a fibrous envelope for the entire 

 mass. The average diameter of 

 the secreting portion of the gland 

 is about 65 fji, of which about 30 /* 

 are contributed by the epithelial 

 lining, and about half as much by 

 the fibrous and muscular tunics ; 

 the remaining 20 n represent the 

 usual lumen. 



The secretion of the sweat- 

 glands varies with the locality and 

 the character of the glands ; in 

 general the secretion of these 



structures occurs in two forms, as the colorless, slightly turbid 

 fluid, devoid of morphological constituents, which is elaborated by 

 the smaller glands and is the sweat proper, and as the thicker oily 

 substances supplied by the large axillary, the circumanal, and the 

 ceruminous glands. The products of these structures consist mostly 

 of water, but contain, in addition, about 1.2 per cent, of solids, in- 

 cluding fat, fat-acids, albuminous matters, urea, and salts in various 

 proportions and combinations. 



The ceruminous glands of the ear and the glands of Moll of 

 the eyelid must be regarded as modified sudoriparous glands, since 

 they closely correspond to the sweat-tubes in structure. 



The total number of sweat-glands of the human body has been esti- 

 mated to be about two millions (Krause) ; they are most numerous 

 on the palms of the hands, in which situation 373 occur within a single 

 square centimetre, and are almost as frequent on the soles of the feet ; 

 the glands are most sparingly distributed over the back and the but- 

 tocks, where less than sixty are contained within one square centimetre. 



Section of coiled part of sweat-gland from 

 human skin : a, a, secreting portion of tubule, 

 cut in various directions ; b, b, parts representing 

 beginning of duct ; c, intertubular conneciive 

 tissue ; d, layer of involuntary muscle inside the 

 basement-membrane ; e, cuticular border. 



