1902.J CARPAL VIBRISS^E IN MAMMALS. 135. 



observations go, in the form which it possesses in the Carnivora, 

 Marsupials, &c. 



But I shall now proceed to urge some facts and suggestions 

 which would tend to show that in the Horse tribe there are traces 

 of this organ present in the well-known " chestnuts " of those 

 animals — callosities on the fore and hind feet or fore feet only. 

 And to do so I must revert to the Armadillo. The condition of 

 this organ in the Armadillo requires some further description, as 

 it differs in certain points from what is to be found in other 

 mammals. As will be seen from the drawing (text-fig. 17, p. 128), 

 the long vibrissse are not so markedly longer than the hairs which 

 clothe the skin generally as is the case with other mammals. The 

 general hairy coveiing of the Armadillo is coarse. In the second 

 place, they are decidedly more numerous and not arranged in a 

 tuft ; they do not, that is to say, apparently spring from the same 

 circumscribed spot. On the contrary, they are borne upon a 

 raised patch of integument which is about half an inch long ; 

 this tract of integument, moreover, is considerably thickened, 

 which marks it oil' fi-om the surrounding integument in a very 

 distinct way. A dissection of the skin in this region shows a 

 nerve supplying this tract of vibrissse-covered skin ; but the nerve 

 is rather small in proportion to its bulk in such an animal as 

 the Coati (text-fig. 20, p. 132). The tract of skin bearing the 

 vibrissse would be quite obvious if it bore no vibrissas at all. It 

 has, too, a hard "feel." Now if this specialization of the pad 

 bearing the vibrissas were to proceed further, it would become a 

 mei-e horny pad and the vibrissse would cease to grow upon its 

 general surface, as with the pads of the foot. They would, so to 

 speak, be driven off or at least to one corner. The resulting state 

 of affairs would be such as is represented in the Lemur, where 

 (yLemur catta) tlieTe is a horny pad, to the side of which is the 

 tuft of carpal vibrissfe ; a still further specialization would of 

 course bring about the conditions which I and Mr. Sutton have 

 shown to obtain in Hapalemihr griseus. On the other hand, the 

 disappearance of the tuft of vibrissse would result in a structure 

 precisely like the "chestnut" on the fore limbs of the Equidse. 

 It appears to me that the condition of the sensory organ upon 

 the wrist of Dasyjjus villosus distinctly suggests a possible origin 

 for the " chestnuts " of the Horse tribe, which have been variously 

 explained, but not in this way. There is every a priori likelihood 

 of finding traces in the Ungulata of this widely spread organ, and, 

 as already stated, in the primitive ungulate Hyrax they actually 

 exist, in a but slightly modified form. The difficulty caused by 

 the fact that the hind limbs in the true Horses have also " chest- 

 nuts " is removed by the occurrence in Petaurus sciureits of these 

 organs on the hind as well as on the fore limbs \ 



1 It must be borne in mind, however, that in the horse the "chestnuts" of the 

 hind limb are upon the ankle, those of the fore limb above the wrist. The latter 

 position is that of other mammals. 



