ORGAN OF TOUCH IN MAMMALIA. 187 



which is thin, soft, or papillose, exalts its sensibility ; as, for 

 example, in the lips, at the end of a teat, of a clitoris or penis, 

 and to a degree, in the latter instances, approaching the cha- 

 racter of a special sensation. In land-mammals the hair is not 

 developed on the more sensitive surfaces, and the skin there is 

 commonly thinnest. Man exemplifies the maximum of dermal 

 sensibility through the comparative thinness and general naked- 

 ness of his integument. That which covers the broad tips of the 

 fingers is unusually vascular, and richly supplied with penicellate 

 plexuses of nerves : the filaments to the papillae seem to terminate 

 in condensed corpuscles of cellular tissue, certainly continuous 

 with the terminal neurilemma the ' corpuscula tactus ' or ( axile' 

 corpuscles, occupying, each, the centre of a papilla. The 

 digital papillae average in Man T ^th of an inch in length, w r ith 

 a basal diameter of Y y^-th of an inch ; they are conical with a 

 rounded apex. Each is supplied by a branch from the arterial 

 plexus of the cutis : they do not project, like the lingual papillae, 

 beyond the epithelial level. Tactile papillae, usually of a larger 

 or coarser kind, are developed on the digital integument in Quad- 

 rumana, and on the naked surface of the skin of the prehensile 

 tail (Ateles); also on the naked terminal integument of the nose 

 of quadrupeds, especially when, as in the pig, mole, and shrew, 

 it is produced as an exploratory ( snout,' fig. 297, or forms, as 

 in tapirs and elephants, a ( proboscis.' Certain of the papillae 

 of the prominences commonly so called, fig. 149, on the surface 

 of the tongue are tactile, but whether also gustatory, or distinct 

 from those that taste, is undetermined. The marginal integument 

 of the upper and lower mandible of the Ornithorhynchus is 

 eminently tactile. 



Certain hairs acquire a size, length, firmness, and such a con- 

 nection of their sclerous basal capsule and bulb with sensory 

 nerve-filaments, as to receive very delicate impressions by contact 

 with extraneous objects or impulse : they are termed ( vibrissae ' 

 or whiskers. The bulb and capsule } of the whisker is sunk deep 

 into the substance of the derm, and is inclosed in a sclerous cap- 

 sule, 2 which in the walrus 3 shows an almost cartilaginous hard- 

 ness. The bristles, in that marine carnivore, have the firmness 

 of horn, and act as a staff, in a way analogous to that held and 

 applied by the hand of the blind man. 4 The varieties in the 



1 xx. vol. iii. (1835), pi. xliii.. fig 7,f, ' internal tlieca.' 



2 Ib. e, 'external theca.' 3 Ib. fig. 10. 



4 The analogy of this action in aquatic mammals to the impressions conveyed by- 

 vibrations continued from the surrounding medium along the gelatinous contents ot 



