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Show 1902.] CARPAL VIBBISS2E IN MAMMALS. 133 summary of the facts at my disposal, the vibrissa were only to be found in the fore limbs. In some cases I admit I did not examine with great care the tarsus as well as the carpus. But after finding that in one species (illustrated in text-figs. 18, 19, pp. 130, 131) both fore and hind limbs showed a, precisely similar tuft of vibrissa^, I naturally examined other animals that came m y way. In Petaurus sciureus, in fact, this tuft of sensory hairs is present on both pairs of limbs, occupying a corresponding position in each. There was no difference that 1 could detect in the arrangement or structure of the vibrissa? in the two limbs. The case appeals to m e to be simply another instance of structures appearing in one pair of limbs being repeated in the other,-just as the horny spine-like outgrowths of the wrist of Hapalemur griseus are found on the ankle of Galago garnettil. The accompanying illustration (text-fig. 20, p. 132) shows the tuft of carpal vibrissa? in a Coati with the skin-flap removed and the muscles partly dissected. In this animal the tuft consists of six long black hairs, the implantation of which on the skin is shown in the drawing. The roots of these vibrissa? are provided with a nervous supply in the shape of a strong branch leaving the main nerve of the arm just opposite to the tuft, and ending after a short course without any sensible diminution of thickness and without any branching visible to the naked eye. This marked nervous supply to the carpal sense-organ is not, however, invariably found. The most aberrant condition of this carpal organ in all the animals which I have examined exists in Hyrax. In this Ungulate, the only Ungulate in which I have been able to detect the organ at all, I could only find it on one of the two fore limbs ; and on that limb, the right, it was represented by only two long hairs, one being situated in the normal position which the tuft occupies in other mammals, and the other placed some way behind this. On carefully dissecting away the skin the roots of the hairs were exposed, and their great size enabled it to be seen that there were two of them, though only one hair was visible externally. In the case of the posterior tuft I could find but one hair-bulb. This state of affairs is shown in the drawing exhibited herewith (text-fig. 21, p. 134). The most careful examination faded to show any nerve-branch supplying the roots of the vibrissa?. I have no doubt that minute microscopic threads exist; but there is nothing that can be detected with the naked eye to be seen ; and I think that it could hardly have been overlooked. Now it appears to m e that we have in this animal a case of commencing retrogression of the organ in question. It can hardly be denied that Hyrax stands at least nearer to the base of the Ungulate series than do the Perissodactyla or the Artiodactyla. Therefore it is not surprising to find in Hyrax traces of a structure that has entirely disappeared in the more specialized forms; and in effect > See Beddard, P. Z. S. 1881. p. 393, and ibid. 1901, vol. i. p. 272. |