188 ANATOMY OF VEETEBBATES. 



character of vibrissa? are, in like manner, adapted to receive and 

 communicate the impressions affecting particular species, or 

 special localities eyebrows, cheeks, lips where they may be de- 

 veloped. Whiskers are long and fine in the crepuscular cats ; 

 still longer in the nocturnal aye-aye. 



The corpuscular thickenings of the neurilemma with the soft 

 centre to which the terminal nerve-filament may be traced 

 ('Pacinian bodies,' vol. i. p. 324, figs. 213, 214) are related to 

 the present simplest and most diffused kind of sensation. The 

 degree in which any given part of integument can discriminate 

 two distinct contacts is shown by the intermediate distance at 

 which they begin to be felt as a single impression. Obtuse 

 points of a pair of compasses, e. g. applied, to the skin, with suc- 

 cessive degrees of approximation until they feel as one point, 

 have shown the different discriminating power of different parts 

 of the surface of the human body, which, in the main, is expressive 

 of the degrees of general sensibility of such parts. The following 

 are instances in the decreasing ratio of acuteness of feeling or 



O " 



discriminating power : tip of the tongue, palmar surface of ter- 

 minal joint of finger, red surface of lip, tip of nose, palm of hand, 

 skin of cheek, sole of foot (parts of), buttocks and adjoining part 

 of thighs, loins, back. l 



As the seats of special sense are almost devoid of common sen- 

 sation, so surfaces with peculiar kinds of the latter, as the teat, 

 penis, or the skin of the axilla, palm and sole susceptible of the 

 sensation called f tickling,' have low degrees of tactile discrimina- 

 tion. For the phenomena and relations of the sense of tempera- 

 ture, see LXVIII". 



The horn-cased feet of the Ungulates, devoid of prehensile 

 po\ver, need no nicety of touch ; but they have a sensitiveness by 

 which the degrees of firmness of soil, e. g., may be appreciated ; 

 and this is due to the disposition of a highly vascular and nervous 

 stratum into fine and long villi on the sole, and into numerous 

 close-set lamellaB, fig. 17, 2 17, which, interdigitating with soft 

 horny lamella? in the inner surface of the wall of the hoof, relate, 

 at the same time, to its renewal and firm attachment to the ter- 

 minal phalanx. 



In Cetacea the peripheral surface of the derm is produced into 

 fine and long papillae, highly vascular, and connected with nerve- 



the tubes whose buried base receives the sensitive nerve, in certain Fishes (vol.i 

 p. 325), was fii\st appreciated by HUNTER, xx. vol. iii. p. 55. 



1 For further details and gradations see LXVIII". vol. ii. p. 516, and LXIX". 



2 xx. vol. iii. p. 58, preps, nos. 1410-1413. 



