THE APPENDAGES OF THE SKIN 1163 



The shaft of the hair (scapus pili) (Fig. 877) consists of a central pith or medulla, 

 the fibrous part of the hair, and the true cuticle externally. The medulla (sub- 

 stantia mcdullaris pili) occupies the centre of the shaft and ceases toward the 

 point of the hair. It is usually wanting in the fine hairs covering the surface of 

 the body, and commonly in those of the head. It is found in the shafts of all thick 

 hairs and in the deeper parts of the root of most hairs. It is more opaque and 

 deeper colored when viewed by transmitted light than the fibrous part; but when 

 viewed by reflected light it is white. It is composed of rows of polyhedral cells, 

 which contain granules of eleidin and frequently air spaces. The fibrous portion 

 or cortical substance of the hair (substantia corticalis pili} constitutes the chief part 

 of the shaft; its cells are elongated and unite to form flattened fusiform fibres. 

 Between the fibres are found minute spaces which contain either pigment granules 

 in dark hair or minute air spaces in white hair. In addition to this there is also a 

 diffused pigment contained in the fibres. The cells which form the outer hair 

 membrane or true cuticle (cuticula pili} consist of a single layer which surrounds 

 those of the fibrous part; they are converted into thin, flat scales, having an imbri- 

 cated arrangement. 



Connected with the hair follicles are minute bundles of involuntary muscle 

 fibres, termed Arrectores pilorum (mm. arrectores pilorum) (Figs. 868 and 877). 

 They arise from the superficial layer of the corium, and are inserted into the outer 

 surface of the hair follicle, below the entrance of the duct of the sebaceous gland. 

 They are placed on the side toward which the hair slopes, and by their action 

 elevate the hair. 1 When the hair is elevated a depression forms over the seat of 

 origin of the muscle, and the parts about the hair are elevated. This condition 

 is known as goose skin. It is probable that the contraction of these "muscles aids 

 in emptying sebaceous glands. 



Bloodvessels and Nerves (Fig. 868). A hair follicle possesses n rich network of capillaries 

 about the hyaline membrane, and capillary loops pass to the papilla. We have little knowledge 

 as to nerve terminations of the human hair. "In other mammals the nerves end below the 

 sebaceous glands. Myelinic fibres lose their ravelin sheaths, divide, and penetrate to the hyaline 

 membrane. Here some of the branches encircle the hair, while others end freely on the hyaline 

 membrane as naked axis cylinders. These branch regularly and run parallel to the long axis of 

 the hair." 2 



The Sebaceous Glands (glandulae sebaceae) are small, sacculated, glandular 

 organs, lodged in the substance of the corium. They are found in most parts of 

 the skin, but are especially abundant in the scalp and face; they are also very numer- 

 ous around the apertures of the anus, nose, mouth, and external ear, but are want- 

 ing in the palms of the hands and soles of the feet. Each gland consists of a 

 single duct, more or less capacious, which terminates in a cluster of small secreting 

 pouches or saccules. The sacculi connected with each duct vary in number, 

 as a rule, from two to five, but in some instances may be as many as twenty. 

 They are composed of a transparent, colorless membrane, enclosing a number 

 of epithelial cells. Those of the outer or marginal layer are small and polyhedral, 

 and are continuous with the lining cells of the duct. The remainder of the sac 

 is filled with larger cells, containing fat, except in the centre, where the cells have 

 become broken up, leaving a cavity containing their debris and a mass of fatty 

 matter, which constitutes the sebaceous secretion. The orifices of the ducts 

 open most frequently into the hair follicles, but occasionally upon the general 

 surface, as in the labia minora and the free margins of the lips. On the nose 

 and face the glands are of large size, distinctly lobulated, and often become much 



1 Arthur Thomson suggests that the contraction of these muscles on follicles which contain weak, flat hairs 

 will tend to produce a permanent curve in the follicle, and this curve will be impressed on the hair which is 

 moulded within it. so that the hair, on emerging through the skin, will be curled. Curved hair follicles are 

 characteristic of the scalp of the Bushman, 



- Histology and Microscopic Anatomy. By Ladislaus Szymonowicz. Translated and edited by John Bruce 

 .Macf'allinn, M.I). 



