456 CHORDATA. 
forms the outer root-sheath ; the mucous layer inside it is 
known as the zz#er root-sheath and upon its surface is pro- 
duced the sheath-cuticle. In a similar manner the hair 
itself has a central medulla produced from the basal 
epithelium, a cortex around it, formed by the mucous layer, 
Fig. 321.—DIAGRAMMATIC SECTIONS ILLUSTRATING THE 
DEVELOPMENT OF A HAIR. 
€ D 
(ROANEOUS 
4 pvcous 
ae a 
ee | { 
(amin GERM, 
Se yee, [ epitHELUn 
a BASAL @PITHELI 
mer 
~~ 
: OyreR RooT-sHEATH— 
fi ANNER ROOT 
\ 
} mene 
OUTER ROOT swe gf 
f 
smeneiesmnrn Ls 
Re 
Wer 
SHEATH CUTUCLE 5 
A, The hair-germ. _B, Formation of papilla and axis. C, Formation of cuticular 
cylinder. D, Splitting of cuticular cylinder and formation of hair. 
E, Transverse section of D. 
and outside this a thin Aair-cuticle. The cortex becomes 
eventually transformed into ceratin and usually carries the 
pigments which give hairs their peculiar coloration, whilst 
the medulla becomes a spongy network of cells which often 
