1292 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS 



The number of hairs to the square centimetre varies in different parts of the body and also in 

 the same situation with the individual and with differences in race, colour and diameters. 



The hairs are most numerous on the head, ranging from 170 to 300 to the square centimetre 

 at the vertex. They are less numerous on other parts of the body, varying from 23 to 44 (per 

 square centimetre) on the chin, and from 24 to 80 on the forearm. The greatest number is 

 found with blonde hair, the next with brown, then black, and the least with red hair. 



The structure of the hair. — Each hair consists of a shaft [scapus pili] (fig. 1050) 

 projecting from the free surface of the skin to end (unless broken or cut) in a 

 conical end [apex pili], and of a root [radix pili], imbedded in the case of the lanugo 

 hair in the corium and of the larger hairs at various depths in the subcutaneous 

 tela. Surrounding the root is a downgrowth of the skin known as the follicle 

 [folliculus pili]. 



Fig. 1051. — ^Longitudinal Section of a Hair Ready to Fall out, with Follicle for New 



Hair. (X30) (From Toldt's Atlas.) 

 Shaft 



— • Root 



Dermal coat of hair -follicle 



Orifice of sebace- X^ ^ 

 ous gland |VJ 



Epidermal coat of hair -follicle 



-Hair-knot (modified hair -bulb) 



/ 



Papilla pili 



_^ Fundus folliculi pili 



The root of the hair at its deepest parts swells to from one and one-half to three 

 times tlie diameter of the shaft forming thus the bulb [bulbus pili] (fig. 1050). 

 Tiie hull) is hollow and a vascular connective-tissue process, the hair papilla [papilla 

 pili] (figs. 1050, 1051) extends from the deepest part of the follicle into the cavity 

 in its base. The follicle consists of an external connective-tissue portion formed 

 by the corium, the theca folliculi and an internal epithelial portion belonging to 

 the epidermis and divided into two portions, the inner and outer root sheaths 

 (fig. 1050). 



The theca of the follicle is composed of an outer loose longitudinal and a middle circular 

 layer of connective tissue and an inner l)aHemont mombranc. The outer root sheath is directly 

 connected with the stratum gorminativum of tlic^ epidermis. In its deei)or part it consists of 

 several layers of cells but of only one near the surface. The inner root sheath lias been divided 

 into three laycns. At the junction of the outer and middle tiiirds of the follicle of most of the 

 hairs, the ducts of usually two or more sebaceous glands connect with the space between the hair 



