XXIX.] THE SKIN. 323 



liquely from the deeper part of the hair-follicle to the upper part of 

 the corium (fig. 309). 



7. T.S. of Hair-Follicles (Scalp). 



(a.) (L) In the human scalp the hair-follicles are arranged in 

 groups of three or four, with interweaving strands of connective 

 tissue between them. The various coverings dermic and epi- 

 dermic can now be distinctly seen, especially if the section be 

 through the lower half of the hair-follicle. 



(6.) (H) Observe both V.S. and T.S. to see the structural ele- 

 ments forming the outer coverings of a hair-follicle. 



(i.) The inner root-sheath consists of an outer layer of cells, clear 

 and non-nucleated Henle's layer and an inner nucleated layer 

 Huxley's layer. Both are best seen in T.S. 



(c.) The hair has a cuticle, while the hair itself may or may not 

 have a medulla. 



Carefully compare the structures of the hair-follicle in the T. and 

 V. sections. 



(d.) The sebaceous gland, its acini lined by cubical cells, contain- 

 ing fat, and rendered clear by the balsam. 



The epithelium of the duct continuous with that of the outer 

 root-sheath. 



8. Sebaceous Glands. (a.) Harden the alae of the nose of a 

 new-born child in corrosive sublimate. (6.) Or the ala of nose or 

 adult scrotum in picro-sulphuric acid (2-3 hours). Stain all 

 with haematoxylin. Large sebaceous glands opening free on the 

 surface without any hair-follicle are found. In other situations 

 they open into the neck of a hair follicle. They are saccular 

 glands with oval alveoli, which lead into a short duct. The alveoli 

 are lined by a layer of polyhedral cells, and internal to this are 

 larger cells containing fatty matter. The sebaceous secretion is 

 formed by these cells undergoing disintegration, and liberating the 

 fatty matter they have formed. They are developed from the outer 

 root-sheath. In balsam they are clear, but in water they appear 

 dark and granular. 



9. Human Hair (H). Place it in water, cover, and examine. 

 A rod-shaped body covered by a single layer of thin, non-nucleated 

 transparent imbricate scales arranged transversely cuticle. In 

 some hairs it is seen merely as fine, more or less transverse, 

 irregular, or wavy lines joining each other. These indicate where 

 the one cell overlaps the other. The substance or cortex of the 

 hair, composed of horny, fibrous substance hair fibres finely 

 striated longitudinally, with, in some hairs, fine pigment-granule? 

 scattered along the course of the hair between the hair-fibres. In 

 some hairs a darker central core or medulla composed of polyhedral 

 cells. 



