428 



THE SKIN. 



has a much wider lumen (fig. 490). The duct, as it passes through the epidermis, 

 is twisted like a corkscrew, that is, in parts where the epidermis is sufficiently thick to 

 give room for this (fig. 466) ; lower down it is straight or but slightly curved. Some- 

 times the duct is formed of two coiled-up branches which join at a short distance 

 from the gland. The tube, both in the gland and where it forms the excretory 

 duct, has a vascular investment of connective tissue, continuous with the corium, 

 and reaching no higher than the surface of the true skin, and within this invest- 

 ment consists of a thin membrana propria and an epithelial lining. The epithelium in 

 the gland proper is formed of a single layer of cubical or columnar cells (often con- 

 taining brownish pigment) and, in the duct, of two or more layers bounded next the 



Fig. 490. SECTION OF A SWEAT-GLAND IN 



THE HUMAN SKIN. (E. A. S. ) 



a, a, secreting tube in transverse section ; 

 b, part of secreting tube seen from above 

 (surface focus) ; c, c, efferent tube (com- 

 mencing duct) ; d, intertubular connective 

 tissue with blood-vessels. In the section 

 across the secreting tube 1 is the basement 

 membrane ; 2, the muscular fibres cut across ; 

 3, the secreting epithelium lining the tube. 



lumen by a fine cuticular lining. 

 The epithelium of the duct is con- 

 tinuous with the epidermis, the 

 twisted part of the duct being merely 

 a channel excavated between the 

 epidermis cells. In the proper 

 secreting portion of the gland be- 

 tween the epithelium and the base- 

 ment membrane, is a layer of longi- 

 tudinally and obliquely disposed 

 fibres which are generally described as plain muscular fibres, although the evidence 

 of their muscular nature is not conclusive (Tartuferi). They vary in amount 

 and are best marked in the larger glands, where they form a complete layer ; 

 in smaller glands the layer is incomplete, and in the smallest the fibres may be 

 altogether lacking. According to Bonnet the muscular layer is least developed in 

 those parts of the skin which are most subject to the tension produced by contrac- 

 tion of ordinary muscles, and in those glands which yield a more fluid secretion. 

 The fibres are absent in the duct. The latter is often coiled two or three times before 

 leaving the gland, but its coils are distinguished from those of the gland proper by 

 the differences above mentioned. The secreting cells of the sweat-glands show the 

 peculiar striated structure characteristic of many gland-cells, and minute canals or 

 clefts are said to pass from the lumen of the tube between the opposed surfaces of 

 the cells (Ranvier). In the large glands in the axilla, at the root of the penis, on 

 the labia majora, and in the neighbourhood of the anus, the layer of so-called 

 muscular fibre-cells between the epithelium and basement membrane is very well 

 marked. In the larger glands, also, the duct is rarely simple, being more usually 

 parted by repeated dichotomous division into several branches, which before ending 

 give off short csecal processes ; in rare cases the branches anastomose. On carefully 

 detaching the cuticle from the true skin, after its connection has been loosened by 

 putrefaction, it usually happens that the cuticular linings of the sweat-ducts get 

 separated from their interior to a certain depth, and are drawn out in form of short 

 threads attached to the under surface of the epidermis. The coils of the gland-tube 

 are loosely held together by connective tissue (fig. 490, d), which may form a sort of 



