10 CARPAL SENSE ORGAN CHAP. 



and for the horns of the Rhinoceros. It is a matter of common 

 knowledge that upon the head of various animals, e.g. the 

 Domestic Cat, long and sensitive hairs are developed, which are 

 connected with the terminations of nerves, and perform a sensory, 

 probably tactile function. These occur on the snout, above the 

 eyes, and in the neighbourhood of the ears. It is an interesting 

 fact that a tuft of quite similar hairs occurs on the hand of 

 many mammals close to the wrist, which, at least in the 

 case of Bassaricyon, are connected with a strong branch from the 

 arm-nerve. These tufts also occur in Lemurs, in the Cat, various 

 Rodents and Marsupials, and are probably quite general in 

 mammals who " feel " with their fore-limbs ; in which, in fact, 

 the fore -limbs are not exclusively running organs. That the last 

 remaining hairs of the Cetacea are found upon the muzzle, is 

 perhaps significant of the importance of these sensory bristles. 

 The entire absence of hairs is quite common in this order, 

 although traces of them are sometimes found in the embryo. 

 The Sirenia, too, are comparatively hairless, as are also many 

 Ungulates. Whether the presence of blubber in the former case 

 and the existence of a very thick skin in the latter animals are 

 facts which have had anything to do with the disappearance of 

 hair or not, is a matter for further inquiry. 



The intimate structure of the hair varies considerably. The 

 variations concern the form of the hair, which may be round in 

 transverse section, or so oval as to appear quite Hat when the 

 hair is examined in its entirety. The substance of the hair is 

 made up of a central medulla or pith with a peripheral cortex ; 

 the latter is scaled, and the scales are often imbricated and 

 with prominent edges. The amount of the two constituents also 

 differs, and the cortex may be reduced to a series of bands 

 surrounding only tracts of the enclosed pith. In the hair is 

 contained the pigment to which the colour of mammals is 

 chietiy due. Tracts of brightly-coloured skin may exist, as in 

 the Apes of certain genera ; but such structures are not general. 

 The pigment of the hair seems to consist of those pigmentary 

 substances known as melanins. It is remarkable to find such an 

 uniform cause of coloration, when we consider the great variety 

 of feather-pigments found in birds. The variations of colour 

 of the hair of mammals are due to the unequal distribution of 

 these brown pigments. There are very few mammals which can 



