582 



INTEGUMENTARY SYSTEM 



consists of a shaft and a root (fig. 273A). The hair shaft is composed, when 

 viewed in transverse section, of three regions of modified cells or products 

 (fig. 273B). The innermost, central (axial) portion ofthe shaft is the medulla. 

 It is composed of shrunken, cornified cells separated by air spaces. Surround- 

 ing the medulla, is the cortex, constructed of a dense horny substance inter- 

 spersed with air vacuoles. External to the latter is the cuticle, made up of 

 thin, cornified, epithelial cells with irregular outlines. The cuticle is trans- 

 parent and glassy in texture. The pigment or coloring substance is contained 

 within the cortical and medullary portions of the hair. Hair color is dependent 

 upon two main factors: 



( 1 ) the nature and quantity of pigment present and 



(2) the amount of air within the cortex and medulla. 



In some hairs, a distinct medullary portion may be absent. 



While the shaft of the hair represents a cornified modification of epidermal 



EPI DE RMIS 



ARY AREA 

 CORT CAL SUBSTANCE OF 

 CUTICLE OF HAIR 



TERNAL ROOT SHE 

 CUT CLE 



XLEY S LAYER 

 HENLF S 



\_ 



HYPODERMIS 



SUBCUTANEOUS 



LAYER OR 



SUPERFICIAL 



FASCIA 

 CONTAIN ING 

 FATTY TISSUE 







CONNECT VE TISSUE 

 GLASSY MEMBRANE 

 EXTERNAL ROOT SHEATH 



Fig. 273. Diagrams of hair and follicle. (B redrawn from Maximow and Bloom, 

 1942. A Textbook of Histology. Saunders, Phila., slightly modified.) (A) Diagram- 

 matic representation of the hair shaft and follicle in relation to skin. (B) Transverse 

 section of hair shaft and follicle in skin of a pig embryo. 



