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, eg. 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-lmbs 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 flat 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 
chiefly 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 
