660 
Proceedings of the Royal Society 
That part of the hair which is contained within the follicle, and 
thus imbedded in the skin, forms the root of the hair. The hair 
decreases in diameter towards the month of the follicle. The free 
portion of the hair, or that which projects beyond the mouth of the 
follicle and outside the skin, is termed the shaft or stem, and forms 
the true hair. The shaft is usually round or oval, in section 
becoming smaller in diameter towards the unattached extremity, 
where it terminates when uncut in a point of more or less 
fineness. 
Occasionally there are two or more points. The hairs vary very 
much both in length and diameter in different parts of the body 
both of man and the lower animals. The whole surface of the hair 
is covered over with a cuticle or coating of fine imbricated scales, 
the free margins of which are always towards the point of the hair, 
and these upwardly projecting edges give rise to a series of waved 
or serrated transverse lines, which can be distinctly seen under the 
microscope, especially after reagents have been used. The form of 
these scales is very diverse, and the distinctions very marked 
between different classes of animals and even between those of the 
same class. Within this scaly covering is a fibrous substance 
termed the cortical portion of the hair, and which in many hairs 
forms nearly the whole of the stem, but which in others is replaced, 
so far as the central portion of the hair is concerned, by a substance 
of a more distinctly cellular structure which forms a medulla or pith. 
Upon the cortical portion of the hair, its firmness, strength, and 
elasticity depends. In coloured hairs the cortex presents numerous 
longitudinal striae or interrupted dark lines and dots, but in colourless 
hairs these are not easily detected, and are only visible as areas of 
unequal transparency. This portion of the hair when broken up 
by the use of suitable reagents, reveals elongated spindle-shaped 
cells with uneven surfaces, and a flattened and irregular angular 
section, often curved from their mutual pressure resulting from 
aggregation within the shaft of the hair. These ultimate cells vary 
in every dimension very much in every kind of hair, and often 
present distinct nuclei and irregular cavities which are filled with 
air. The medulla or pith when it exists in any hair, is also formed 
of clusters of cells ; but in place of being spindle-shaped like those 
in the cortex, they are usually more rounded in form, although 
