692 SEBACEOUS GLANDS. [BOOK n. 



stratum granulosuin and lucidum respectively. The dermis of the 

 wall of the follicle is at the same time developed into an outer 

 layer with bundles of connective tissue disposed chiefly longitu- 

 dinally, and an inner layer of peculiar nature, the arrangement of 

 which is transverse, and which at least simulates, if it really be not, 

 a muscular transverse coat. Between this dermis of the follicle 

 and the outer root-sheath or Malpighian layer is a very conspicuous 

 definite hyaline basement membrane, so thick that it presents a 

 very easily recognized double contour. 



At the bottom of the follicle the dermis of the wall of the 

 follicle is continuous with the substance of the (dermic) papilla, 

 while the outer root-sheath or Malpighian layer which here 

 becomes extremely thin, and reduced to one or two layers, is 

 reflected over the papilla, and there expands again into a mass of 

 cells, which like the cells of the Malpighian layer in the rest of 

 the skin multiply, and by their multiplication give rise to the 

 corneous body of the hair. It is said that in those hairs which 

 possess a medulla the vertically disposed lowermost cells of the 

 Malpighian layer are at the actual summit of the papilla continued 

 upwards in the axis of the hair, as the medulla. 



The layer of Henle, following the Malpighian layer or outer 

 root-sheath on which it rests, is similarly reflected and forms over 

 the hair a single layer of flat transparent imbricated scales known 

 as the cuticle of the hair. Huxley's layer, similarly reflected, forms 

 a similar layer of similar scales, but this is considered as belonging 

 to the root-sheath and is called the cuticle of the root-sheath. 



Just where the corneous layer abruptly leaves off in the 

 upper part of the hair follicle, a sebaceous gland opens into the 

 cavity of the follicle on each side of the hair. Each gland consists 

 of a short rather wide duct which divides into a cluster of some- 

 what flask-shaped alveoli. The basement membrane, both in the 

 alveoli and in the duct, is lined with a layer of rather small cubical 

 cells continuous with the layer of perpendicularly disposed cells 

 which form the innermost layer of the outer root-sheath as of the 



jhian layer of the skin generally. This layer of cells leaves a 

 wide lumen both in the alveoli and in the duct; this lumen, 

 however, is occupied not as in other glands with fluid, but with 

 cells. Both alveoli and duct in fact are filled with rounded or 

 polygonal cells which may be regarded as modified cells of the 

 Malpighian layer. The whole gland indeed is a solid diverticulum 

 of the Malpighian layer. 



In the alveoli the cells next to the layer of cells immediately 

 lining the basement membrane, though larger than these, resemble 

 them in so far that each consists of ordinary cell-substance sur- 

 rounding a nucleus of ordinary character. The more central cells 

 are different ; their cell-substance is undergoing change, numerous 

 granules or droplets, some of them obviously of a fatty nature, make 

 their appearance in them, and the nuclei are becoming shrunk 



