HAIR. 263 



ART. XIII. HAIR. 



WE now come to the description of another epidermic modi- 

 fication, viz. hairs : these, however, are much more complex 

 in their structure than any which have been hitherto described, 

 and are less obviously derived from the epidermis. 



As in the case of most of the solids described in this 

 work, we shall first discuss the different particulars relating 

 to form and size, and next proceed to the description of 

 structure. 



FORM OF HAIRS. 



Hairs consist of two parts, a root and a stem : in speaking 

 of the form of hairs, reference is made to the latter. Hairs 

 then are elongated, and more or less cylindrical develop- 

 ments of the epidermis. They depart, however, in most 

 cases from the character of a true cylinder in two re- 

 spects ; first, they are not perfectly spherical, but are seen 

 to be, when viewed transversely, either oval, flattened, 

 or reniform (see Plate XXIX.) ; and secondly, they are 

 not of equal diameter throughout, being thickest at about 

 the junction of the lower and middle thirds of the stem, 

 of smaller diameter from this part downwards towards the 

 root, and still more reduced in size as the free extremity 

 is approached, and which, in a hair which has not been 

 recently cut, terminates in a point, the diameter of which 

 is frequently several times less than that of the more central 

 parts of the shaft. (See Plate XXIX.) 



This form is best seen in hairs of medium length, as those 

 of the whiskers, eyebrows, axillae, and pubis, in which also 

 the flattened and oval shapes are principally detected. 



The hairs which approach most closely thjp cylindrical ar 

 those of the scalp, 



