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THE SKIN OR INTEGUMENT. 
The hair follicle (folliculus pili) consists of an oblique or curved—the latter in 
curly hairs—invagination of the epidermis and corium, and, in the case of large 
hairs, extends into the subcutaneous tissue (Fig. 556); some little distance below its 
orifice, the ducts of the sebaceous glands open into it. The portion of the follicle 
derived from the corium (dermic coat) consists of a fibrous sheath of external longi- 
tudinal and internal circular connective tissue fibres, the latter being lined by a 
hyaline layer directly continuous with the basement membrane of the corium. The 
parts of the follicle derived from the epidermis are named the inner and outer root 
sheaths. Below the orifices of the sebaceous gland ducts the outer root sheath is 
formed by the stratum germinativum and stratum mucosum, while above them all 
the epidermal strata contribute to it. The inner root sheath surrounds the cuticle 
Fibrous sheath \ Derived from 
/ Basement membrane f the corium 
Stratum germinativum ) Outer root 
Stratum mucosum  ) Sheath 
Heule’s layer 
\ Inner root 
Huxley’s layer il sheath 
Cuticle 
Section of hair 
Fic. 541.—TRANSVERSE SECTION OF Harr FOLLICLE WITH CONTAINED Hair (highly magnified). 
of the hair, and consists from without inwards of—(a) Henle’s layer, a single stratum 
of nucleated, cubical cells; (b) Hualey’s layer, a single or double layer of polyhedral 
nucleated cells; and (¢) a delicate cuticle, consisting of a single layer of flattened 
imbricated cells, with atrophied nuclei. The bottom of the hair follicle is indented 
by a vascular papilla (papilla pili), derived from the corium and capped by the 
bulb (bulbus pili) or expanded part of the hair root. The cells of the bulb are 
continuous with those of the outer root sheath, and form the different parts of the 
hair, as well as its inner root sheath. The vessels form capillary loops in the papilla 
of the hair, and send twigs into the outer layer of its fibrous sheath; the inner 
and outer root sheaths and the different parts of the hair are non-vascular. The 
nerves terminate in longitudinal and annular fibrils below the level of the sebaceous 
glands and outside the hyaline layer of the follicle. 
Sebaceous glands (glandule sebace) exist wherever there are hairs, and their 
ducts open into the superficial part of the hair follicles (Fig. 536); the number of 
glands associated with each follicle varies from one to four. On the labia minora 
and mammary areole they open on the surface of the skin independently of hair 
follicles, and in the latter situation undergo great enlargement during pregnancy. 
The deep extremity of each gland expands into a cluster of oval or flask- shaped 
alveoli, which are surrounded “by a basement membrane and filled with polyhedral 
cells containing oil droplets. By the breaking down of the superficial cells, their 
oily contents are liberated as the sebum cutanewm and discharged into the hair 
