324 



NORMAL HISTOLOGY. 



the latter and end at varying levels within the fat-laden subdermal layer 

 (panniculus adiposus). In a general way the follicle may be regarded as a 

 narrow tubular invagination of the epidermis, at the bottom of which the 



. Shaft 



Epidermis 



Sebaceous gland 



Erector 



Sweat gland 



Hair-papilla 



FIG. 367. Section of scalp, showing longitudinally cut hair-follicles. X 14. 



hair is implanted and from the entrance of which the shaft projects. The 

 most contracted part of the follicle, the neck, lies at the deeper end of the 

 relatively wide funnel-shaped mouth of the sac. Closely associated with the 

 hair-follicle, which they often surround, are the sebaceous glands that pour 



their oily secretion at the upper third of the 

 follicle into the space between the shaft and 

 the wall of the sac. 



The Hair-Shaft. In many thick hairs, 

 but by no means in all, three parts can be dis- 

 tinguished the cuticle, the cortex, and the 

 medulla. The latter, however, is usually want- 

 ing in hairs of ordinary diameter, being often 

 also absent in those of large size. 



The cuticle of the hair appears as a trans- 

 parent outermost layer marked by a network 

 of fine sinuous lines, the irregular meshes of 

 which have their longest diameter placed 

 obliquely transverse. These lines correspond 

 to the free borders of extremely thin glassy 

 cuticle-plates that overlie the hair as tiles on a 

 roof, the imbrication involving from four to six 

 layers. The cortical substance, often constituting practically the entire 

 shaft, consists of elongated fusiform cells so compactly arranged that the indi- 

 vidual elements are only distinguishable after the action of disassociating 

 reagents. In addition to the remains of the shrunken nuclei, the hair- spindles, 



FIG. 368. Portion of shaft of hair; 

 h, shaft covered with cuticle ; j, corti- 

 cal substance exposed by removal of 

 cuticle; m, medulla; a, 6, isolated cells 

 of cuticle and cortical substance respec- 

 tively. X 240. 



