108 NORMAL HISTOLOGY. 



parts, the shaft and the root. The shaft comprises the cuticle, or 

 outer, imbricated layer of epithelial cells ; the cortex, or middle lay- 

 er, composed of elongated, horny, epithelial cells, which contain 

 the pigment granules that give color to the hair; and the medulla. 

 which constitutes the central cylinder and is composed of cuboidal 

 cells filled with minute air vesicles which appear as dark granules. 

 These air vesicles also contribute to the color of the hair. The 

 follicle is the receptacle of the hair, produced by the infolding of 

 the epidermis. Above the sebaceous glands it consists of a fibrous 

 coat, stratum lucidum, and stratum corneum, but beneath them the 

 stratum corneum disappears. The root and bulb of the hair exhibit 

 a continuation of the same essential structures as found in the shaft. 

 The papilla is a conical elevation of the corium into the base of the 

 follicle and hair bulb. It contains pigment cells and blood-vessels, 

 which provide nourishment. 



A transverse section of a hair varies in outline with different 

 races. The hair of the Mongolian (Japanese) exhibits a circular 

 outline ; that of a German is oval ; that of a Negro is flattened-ovate ; 

 while that of the Papuan is still more flattened and crescent-shaped. 

 The hair is provided with sebaceous glands, which are of the simple 

 and compound saccular type. These open into the hair follicles near 

 their upper extremity. The sebum, or secretion, which they dis- 

 charge upon the surface of the hair is designed to oil it and keep it 

 in a healthy condition. Each hair is also provided with a muscle, 

 ihearrector pili (composed of smooth muscle fibre), which extends 

 obliquely from the deeper portion of the follicle to the upper por- 

 tion of the corium. 



Sebaceus glands. These are of the simple or compound sac- 

 cular type, and are located in the stratum papillare of the corium. 

 They consist of acini, with secreting cells, and a short duct. 



The sudoriferous glands. The sweat glands are of the simple 

 tubular variety. The coil of the gland is located in the subcu- 

 taneous tissue, and consists of a basement membrane lined with se- 

 creting cells. The excretory duct extends through the corium and 

 epidermis by a sinuous course until it reaches the stratum corneum, 

 when it becomes spiral, terminating upon the surface of the skin 

 in a rounded pit. 



