1899.] 



THE CARPUS OF CTE^OMTS. 



429 



Carpus of Ctenomys, etc. 



Fig. 1. Ctenomys sp. (Br. Mus. No. 97. 10.3.68). Left manus, palmar view. 

 E— radius; r.»2 = radiale marginale. U=u]na ; jb/);-= proximal pisiform ; 

 pd=A\?Xa\ pisiform. — Fig. 2. Ctenomys sp., Prov. Salta (Argentina). Left 

 carpus, palmar view. — Fig. 3. Same specimen as Fig. 2. Left carpus, dorsal 

 view. a=:interphalanKeal dorsal ossicle. — Fig. 4. Mus macleari Thos., jun. 

 Eight carpus, palmar view. r)« = proximal marginal radiale. .r=accessory 

 palmar ossicle of the carpus; sc.(!=" scapholunar." — Fig. .5. Arvicanthis 

 niloticus. Eight carpus, palmar view; rM.pr=proximal marginal radiale ; 

 r.OT^ = distal marginal radiile. — Fig. 6. Lepidolemur microdontia,]. Eight 

 carpus, palmar view. /=lunar ; M^» = ulnare. The bones marked a: and ^ 

 (pisiform) are separated by a short meniscus of connective tissue, which 

 unfortunatelj'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. 



On the dorsal side of the thumb (a, fig. 3), overiappino; the inter- 

 phalangeal articulation, is a lengthened ossicle, attached by a strong 

 ligament to the proximal end of the ungual phalanx, and 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 articu- 

 lations in Mammalia; they will be enumerated hereafter ; but t 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 



