320 



HISTOLOGY. 



outer layer is a loose connective tissue with longitudinal bundles, con- 

 taining elastic fibers and numerous vessels and nerves. The middle layer, 

 which is thicker, consists of circular bundles of connective tissue without 

 elastic fibers. The inner layer together with the basement membrane of 

 the outer epithelial sheath may form a single, transparent hyaline mem- 

 brane. The connective tissue portion of the membrane is sometimes 

 longitudinally fibrous; the epithelial part is homogeneous and provided 

 with small pores. 



The outer epithelial sheath is an inpocketing of the epidermis. The 

 stratum corneum extends to the sebaceous gland; the stratum granu- 

 losum continues somewhat deeper, but only a thinned stratum germina- 

 tivum can be followed to the bulb. 



Connective 

 tissue sheath. 



Longitudinal fiber 



layer. 

 Circular fiber layer. 



Hyaline membrane. 

 Outer epithelial sheath. 



(Henle's layer. 

 Huxley's layer. 



I Sheath and hair cutic- 



ulae. 

 Hair. Cortical substance. 



Medullary substance. 



FIG. 371. FROM A HORIZONTAL SECTION OF THE HUMAN SCALP. X 240. 

 Cross section of a hair and its sheaths in the lower half of the root. 



The inner epithelial sheath extends from the sebaceous gland to the 

 bulb. It begins as a layer of cornified cells below the termination of the 

 stratum granulosum; it is, however, not a' continuation of that layer. 

 Toward the bulb the inner sheath is divisible into three layers. The 

 outer or Henle's layer consists of one or two rows of cells with occasional 

 atrophic nuclei; for the most part they are non-nucleated. The middle 

 or Huxley's layer is a row of nucleated cells, and the inner layer or cutic- 

 ula of the sheath is formed of non-nucleated cornified scales. Toward 

 the bulb both the cuticule and Henle's layer are nucleated and the three 

 layers become indistinguishable as seen in Fig. 372. Kerato-hyalin 

 granules which occur in Huxley's and Henle's layers extend nearer the 

 papilla in the latter. 



