CHAPTER X. 

 THE SKIN. 



The skin covers the entire body and is directly 

 continuous with the mucous membranes of the ali- 

 mentary canal and urogenital organs at their 

 external orifices. It contains sensory nerve endings 

 and in the deeper layers there is a liberal supply of 

 both blood- and lymph- vessels. It is the chief factor 

 in regulating body temperature, and is an efficient 

 mechanical protection to the deeper tissues, while the 

 sweat and sebaceous glands render it an important 

 excretory organ. Hairs and nails represent modi- 

 fications of the superficial layers. It varies consid- 

 erably in thickness, being 4 mm. thick on the palms 

 of the hand and 0.5 mm. over the back and shoul- 

 ders. The color is imparted by pigmentation and 

 the blood supply. The color is characteristic of races 

 and variable in the different parts of the body as well 

 as subject to modification depending on age and dis- 

 ease. The skin moves freely upon the deeper tissues, 

 excepting over bony prominences where it is more 

 firmly attached. On the palm of the hand and the 

 sole of the foot it is also bound down to the subjacent 

 tissues. The external surface presents in places 

 numerous permanent ridges which correspond with 

 rows of underlying papillae, and which in criminals 

 are utilized for the purposes of identification. The 



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