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Show 1899.] THE CARPUS OF CTENOMYS. 429 Carpus of Ctenomys, etc. Fig. 1. Ctenomys sp. (Br. Mus. No. 97. 10. 3. 68). Left manus, palmar view. B-radius; r.w=radiale marginale. U = ulna; ppr= proximal pisiform ; pd - dista,\ pisiform.- Fig. 2. Ctenomys sp., Prov. Salta (Argentina). Left carpus, palmar view.-Fig. 3. Same specimen as Fig. 2. Left carpus, dorsal view. «,=interphalangeal dorsal ossicle.-Fig. 4. Mus macleari Thos., jun. Right carpus, palmar view. r?» = proximal marginal radiale. .r=accessory palmar ossicle of the carpus; set-'1 scapholunar."-Fig. 5. Arvicanthis niloticus. Bight carpus., palmar view; r*w.pr=proximal marginal radiale ; r.w<#=distal marginal radiale.-Fig. 6. Lepidolemur microdon Maj. Bight carpus, palmar view. /= lunar; «<Z« = ulnare. The bones marked x and p (pisiform) are separated by a short meniscus of connective tissue, which unfortunately is made to appear in the figure as a distinct bone.- Figs. 1-3 and 6 slightly over nat. size ; figs. 4 and 5 about double nat. size. I. On the dorsal side of the thumb (a, fig. 3), overlapping* the inter-phalangeal articulation, is a lengthened ossicle, attached by a strong ligament to the proximal end of the ungual phalanx, aud gliding on the capitulum of the second. The anterior and posterior extremities of this ossicle are slightly swollen, the shaft being restricted, so that it somewhat resembles a diminutive phalanx. So-called sesamoid bones have been here and there noticed, as rare occurrences, on the dorsal surface of the phalangeal articulations in Mammalia; they will be enumerated hereafter; but I have nowhere found a mention of an ossicle on the interphalangeal articulation of the thumb. On investigating the matter more closely, I have found the same ossicle constantly in the four species of Mus up to the present examined, including our two common » |