860 



THE SKIN OK INTEGUMENT. 



from without inwards of three parts, viz., cuticle, cortex, and medulla. The 

 cuticle is formed by a layer of imbricated scales which overlap one another from 

 below upwards. The cortex consists of longitudinally arranged fibres made up of 

 elongated, closely applied, fusiform cells, which contain pigment and sometimes air 

 spaces, the latter especially in white hairs. The medulla, absent from the fine 

 hairs of the body generally and from the hairs of young children, forms a central core, 

 which appears black by transmitted, and white by reflected light, and is composed 

 of polyhedral nucleated cells containing pigment, fat granules, and air spaces. 



The hair follicle consists of an oblique or curved the latter in curly hairs invag- 

 ination of the epidermis and corium, and in the case of large hairs extends into the 

 subcutaneous tissue (Fig. 733) ; some little distance below its orifice the ducts of 

 the sebaceous glands open into it. The dermic coat or portion of the follicle derived 

 from the corium consists of a fibrous sheath of external longitudinal and internal 

 circular connective tissue fibres, the latter being lined by a hyaline layer directly 



Fibrous sheath | Derived from 



/ Basement membrane ) the corium 



Stratum germinativum * Outer root 

 Stratum mucosum /sheath 



Henle's layer 

 Huxley's layer 

 Cuticle 



Section of hair 



FIG. 738. TRANSVERSE SECTION OF HAIR FOLLICLE WITH CONTAINED HAIR (highly magnified), 



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 of the hair, and 

 comprises from without inwards (a) Henle's layer, a single stratum L of nucleated 

 cubical cells ; (6) Huxley's layer, a single or double layer of polyhedral nucleated 

 cells ; and (c) a delicate cuticle, composed of a single layer of flattened imbricated 

 cells, with atrophied nuclei. The bottom of the hair follicle is moulded on a 

 vascular papilla, derived- from the corium and capped by the bulb of the hair 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 end in 

 longitudinal and annular fibrils below the level of the sebaceous glands and outside 

 the hyaline layer of the follicle. 



Glandulse Sebaceae. Sebaceous glands exist wherever there are hairs, and their 



