578 



THE SKIN AND ITS APPENDAGES [CH. XXXVIII. 



sists of an outer layer of cells like the Malpighian layer of the 

 epidermis, with which it is directly continuous (outer root-sheath), and 

 of an inner horny layer (inner root-sheath), continuous with the horny 

 layer of the epidermis. The inner root-sheath consists of three layers, 

 the outermost being composed of long, non-nucleated cells (Henle's 

 layer), the next of squarish nucleated cells (Huxley's layer), and the 



third is a cuticle of scales, imbri- 

 cated downwards, which fit over 

 the scales of the cuticle of the hair 

 itself. 



A small bundle of plain mus- 

 cular fibres is attached to each 

 follicle (fig. 437). When it con- 

 tracts, as under the influence of 

 cold, or of certain emotions such as 

 fear, the hair is erected and the 

 whole skin is roughened ("goose 

 skin "). The nerves supplying 

 these muscles are called pilo-motor 

 nerves. The distribution of these 

 nerves closely follows those of the 

 vaso-constrictor nerves of the skin; 



Flo. 441. Sebaceous gland from human skin. 

 (Klein and Noble Smith.) 



their cell stations are in the lateral 

 sympathetic chain. 



The sebaceous glands (figs. 

 437 and 441) are small saccular 



glands, with ducts Opening into FIG. 442. Terminal tubules of sudoriferous or 

 fV.o urvrtaT> -r^^fi' ^-P fV,a Vmir. * rt l sweat-glands, cut in various directions from 



the upper portion or tne nair rol- the sk f n of the pig - s ear . (v. D. Hams.) 

 licles. The secreting cells become 



charged with fatty matter, which is discharged into the lumen of the 

 saccules owing to the disintegration of the cells. The secretion, sebum, 

 contains isocholesterin (see p. 512) in addition to fatty matter. It 

 acts as a lubricant to the hairs. 



The sweat-glands are abundant over the whole human skin, but 

 are most numerous where hairs are absent, on the palms and soles. 

 Each consists of a coiled tube in the deepest part of the dermis, the 



