490 



THE TISSUES. 



tissue, with scattered elongated nuclei, and lined apparently by a 

 basement-membrane, supporting a single, double, or multiple layer 

 of polygonal cells, corresponding to the deep cells of compound 

 conoidal epithelium, except that they generally contain a few fatty, 

 and still more frequently yellowish or brownish, pigment-granules. 

 (Fig. 327, A.) The rest, called the thick-coaled canals, contain be- 



Fig. 327. 



Sweat-ducts. A. One with thin walls and a central cavity, without a muscular coat, from the 

 hand : a, connective investment ; 6, epithelium ; c, cavity. S. A portion of a canal without a cavity, 

 and with a delicate muscular layer, from the scrotum : a, connective tissue ; b, muscular layer ; c, 

 cells which fill the glandular canal, with yellow granules among their contents. Magnified 350 

 diameters. (KiUiker.) 



tween the two layers just described a middle layer of smooth mus- 

 cular fibre-cells running longitudinally. (Fig. 327, S.) This is the 

 case with the large glands of the axilla, of the root of the penis, 

 and the nipple ; and the coecal extremity of the canal is supplied 

 with muscular fibre-cells in the scrotum, labia rnajora, mons veneris, 

 and some other parts. 



The size of the canal varies from gj to gj^, and averages about 

 -$^TJ of an inch. The walls are g^nnr to 7oVo of -an inch thick; the 

 epithelium, ^^TF; and the cavity, or lumen, 3 A<y to raW f an inch. 

 The largest glands have canals 4^ to 2 J F of an inch in diameter, 

 with walls 3^0 of an i nca thick. 



The coils of the proper glands are penetrated by collagenous 

 tissue interspersed with fat-cells; which supports the vessels, and 

 unites the separate convolutions. The arrangement of the vessels 

 is seen in Fig. 138. No nerves have yet been found in the glands. 



2. The sweat-ducts are continuous with the upper end of the 



