444 



EXCRETION 



the epidermis. The coiled or secreting portion of the gland is lined with 

 at least two layers of short columnar cells with very distinct nuclei, figure 306. 

 The lumen is distinctly bounded by a special lining of cuticle. 



The sudoriferous glands are abundantly distributed over the whole sur- 

 face of the body; but are especially numerous, as well as very large, in the 

 skin of the palm of the hand and of the sole of the foot. The glands by 

 which the peculiarly odorous matter of the axillae and groin is secreted form 



a nearly complete layer under the cutis, 

 and are like the ordinary sudoriferous 

 glands, except in being larger and having 

 very short ducts. 



The peculiar bitter yellow substance 

 secreted by the skin of the external 

 auditory passage is named cerumen, and 

 the glands themselves ceruminous glands; 

 but they do not much differ in structure 

 from the ordinary sudoriferous glands. 



The sebaceous glands, figures 305 

 and 306, like sudoriferous glands, are 

 abundant in most parts of the surface of 

 the body, particularly in parts largely 

 supplied with hair, as the scalp and face. 

 They are thickly distributed about the 

 entrance of the various passages into the 

 body, as the anus, nose, lips, and ex- 

 ternal ear. They are entirely absent 

 from the palmar surface of the hand and 

 the plantar of the foot. They are 

 racemose glands composed of an aggre- 

 gate of small tubes or sacculi lined with columnar epithelium and filled 

 with an opaque white substance, like soft ointment, which consists of 

 broken-up epithelial cells which have undergone fatty degeneration. Mi- 

 nute capillary vessels overspread them; and their ducts open on either the 

 surface of the skin, close to the hair, or, which is more usual, directly into 

 the follicle of the hair. In the latter case, there are generally two or more 

 glands to each hair, figure 306. 



The story of the structure and development of such epithelial structures 

 as the hair and nails is best left to the histologist, to whom the student is 

 referred. 



The Excretory Function of the Skin. The function of the skin which 

 is of special interest to this chapter is that of the secretion of the sweat. The 

 fluid secreted by the sweat glands is usually formed so gradually that the 

 watery portion of it escapes by evaporation as fast as it reaches the surface. 



FIG. 307. Sebaceous Gland from 

 Human Skin. (Klein and Noble 

 Smith.) 



