502 DR. C. I. FORSYTH MAJOR ON 



Lagomyidae and Leporidae mentioned above. I am not aware that it has ever 

 been recorded before in lagomorj^hous Rodentia ; while it seems qixite a common 

 element in Mammalia jirovided with a Avell-developed fifth digit, at any rate in 

 E-odentia, Insectivora, and Edentata, and Avas known to the older anatomists. Cuvier 

 mentions it in the Great Armadillo {Priodon (/igcmteus), and describes and figures it 

 as situated laterad of the ulnare and articulatins; with the Metac. V *. In the fio:ure 

 jjublished by .Flower f, it would appear to articulate with the ulnare as well. As to its 

 presence in Rodentia, Cuvier remarks : " Eufin il y a tres souvent aussi au. bord externe 

 du carpe, en dehors du cuneiforme et de lunciforme, un os sumumeraire, petit et lenti- 

 culaire ; on le voit dans le castor, le pore-epic" ^. It is figured in a carpus of the 

 Castor ^. In the ' Lecons d' Anatomic comparee,' mention is again made of this " os 

 surnumeraire " in the Hystrix: " . . . il y a un os surnumeraire entre le jnsiforme et 

 I'os metacarjjien du cinquieme doigt ; il est attache sur I'os crochu" ||. 



Thilenius ^, quoting Cuvier's figure of the Castor carpus, is inclined to consider this 

 ossicle as his (Thilenius's) " ulnare externum " = the ulnar part of Ptitzner's triquetrum 

 bipartitum of the adult, found in the human embryo **. He adds, however : " Infoige 

 der radialen Verschiebung des Carpale (4 + 5) erreicht es indessen audi das Metac. V." 

 The question is whether, when an os vesalianum is ])resent, the hamatum is really 

 displaced, or is not rather in its original position; only secondarily either supjjlanting 

 the vesalianum, or acting in a compensatory manner for it, when the latter is either 

 displaced or has disappeared. When comparing Thilenins's figures 11 and 12 of this 

 " ulnare externum " ff with figures 13 and 11 %%, representing a later stage, the impression 

 is conveyed that in the latter this ulnare externum {ue) has been displaced proximally 

 by the ulnad extension of the hamatum. A secondary jjj'o.rimal displacement of a carpal 

 (or tarsal) would, however, be quite unusual, and Thilenius has expressed some doubt §§ 

 whether the figures mentioned all represent the same bont;. In fig. 11, where ne abuts 

 upon Metac. V, the former element might be Pfitzner's vesalianum (carpo-roetacarpale 8, 

 Thilenius). The text-figure XXXIV of the present paper seems to exclude the 

 possibility, ventilated by Thilenius || ||, tliat '-vesalianum" and "ulnare externum" — 

 which have not yet been found together in the same manus of Man — might represent 

 one and the same bone. The enormous ulnad and volad expansion of the ulnare, 

 as shown for the Lagomorpha in this figure (XXXIV) — which occurs in other Mammals 

 also — leads to the assumption of its being a compound of an ulnare -j- ulnare externum 

 Thilen. The "ulnare externum" ( = ulnar part of triquetrum bipartitum Pfitzn.) would 

 then be the second (central) carpale of the fifth ray (V. 2). 



Meckel has described the os vesalianum in Erinacens -. — " Der lyel hat in der obern, 

 weit breitern Ordnung oier Knochen. Kahn- und Mondbein sind zwar verwachsen, 



* Oss. loss. V. 1, p. 127 (1^23). 



t ' An Introduction to the Osteology of Mammalia,' 3rd ed. tig. IIU " «," p. 307 (1885). 



+ Oss. foss. V. 1, p. 48 (1823). § Ih. pi. ii. tig. lU. 



II Lerons d'Anat. comp. 2de cd. i. p. -127 (1835). 



^r Morph. Arb. (Sohwalbe), v. pp. 508, 509 (1S90). 



** Morph. Arb. v. pp. 473, 474 (1S96). 



tt Morjjh. Arb. v. pi. xxi (1896). ++ Ih. §§ Ih. pp. 489, 508. |i || lb. p. 489. 



