390 THE ORGANS 



are flattened and horny, especially near the surface. Some appear 

 homogeneous, others have a lamellated appearance. They contain 

 pareleidin, a derivative of the eleidin of the stratum lucidum. Nuclei 

 are lost, but in many of the cells can be seen the spaces which the 

 nuclei once occupied. Constant desquamation of these cells goes on, 

 cells from the deeper layers taking their place. 



The color of the skin in the white races is due to pigmentation of 

 the deeper layers of the epidermis. In certain parts of the body pig- 

 mentation of the connective- tissue cells of the derma also occurs. In 

 the dark races all cells of the epidermis are pigmented, although there is 

 less pigment in the surface cells than in the cells more deeply situated. 



Two kinds of glands occur in the skin — sebaceous glands and 

 sweat glands. 



Sebaceous Glands. — These are usually associated with the hair 

 follicles, and will be described in that connection. Sebaceous glands 

 unconnected with hair occur along the margin of the lips, in the glans 

 and prepuce of the penis, and in the labia minora. 



Sweat Glands {glandules sudoriparcB.) — These are found through- 

 out the entire skin with the exception of the margin of the lips, the 

 inner surface of the prepuce, and the glans penis. They are simple 

 coiled tubular glands. The coiled portion of the gland usually lies 

 in the subcutis, although it may lie wholly or partly in the deeper 

 portion of the pars reticularis. The excretory duct runs a quite 

 straight course through the derma, and enters the epidermis in one of 

 the depressions between the papillae. In the epidermis the duct 

 takes a spiral course to the surface, where it opens into a minute pit 

 just visible to the naked eye^the sweat pore (Fig. 264). The coiled 

 portion of the gland is lined with a simple cuboidal epithelium, having 

 a granular protoplasm. In the smaller glands the epithelium rests 

 directly upon the basement membrane. In the larger glands a longi- 

 tudinal layer of smooth muscle cells separates the glandular epithe- 

 lium from the basement membrane. The walls of the ducts consist of 

 two or three layers of cuboidal epithehal cqIIs, resting upon a delicate 

 basement membrane, outside of which are longitudinally disposed 

 connective-tissue fibres. On reaching the horny layer the epithelial 

 wall of the duct ceases, the duct consisting of a mere channel through 

 the epithelium (Fig. 272). 



TECHNIC 



(i) Fix the volar half of a finger-tip in formalin-Miiller's fluid (technic 6, p. 

 7) or in absolute alcohol. Curling may be prevented by pinning to a piece of 



•^■. 



