FOSSIL AND RECENT LAGOMORPHA. 503 



allein das grosse dreieckige Eein triig-t aussen und vorn einen kleinen, runden Knocben 

 cingelenkt, den man ein zwcites Erbsenbein nennen kann. Von den vier vordern 

 ist das Ilakenbein weit kleiner als gewobnlich, und das dreieckige stosst daher aussen 

 betrachtlicb ^veit an den fiinften Mittelhandknochen" *. 



Owen mentions the same ossicle in the Hedgehog, but more distally : — " A sesamoid is 

 attached to the outside of tlie base of the metacarpal of the digitus minimus " f. In 

 a left carpus of Erhiaceiis rnropfPiis lying before me, the ossicle articulates with both 

 the ulnarc and Metac. V, the facet for the latter being smaller and, as in Prlodoii, 

 situated ulnad from the ulnare. The same bone is mentioned in Gymimra by Dobson |. 



Eeferringto this ossicle, Leboucq says : — " Ce qu'on appelle 2'" pisiforine, existant chez 

 quelques mammiferes (h(?risson, tatou, etc.), n'est qu'un sesamoide developpe dans le 

 tendon de Textenseur cubital du carpe" §. It may be a matter of surprise that, in the 

 same chapter in whicli Leboucq insists with strong argunu>nts tliat the pisiform cannot 

 he classed among " les os sesamoides," he casts aside with a few passing words this 

 equally imjioitant bone. The exj)lanatioa is to be found in the words " chez quelques 

 mammifei'es ; " the autlior being evidently not sutficientiy acquainted with the " os 

 vesalianum." 



Having placed the facts before the reader, I have now to sum up. All the attempts 

 (Leboucq, Baur, Rosenberg, Pfitzner, Thilenius) to trace ontogenetically the pre- 

 sumed fusion of carpalia 4 and 5 to form the " hamatum " have confessedly failed. 

 Geijenbaur explains this negative result by sujiposing that the ^lammalia inherited 

 the "hamatum," from lower Vertebrates. This leads him U) the assumption that the 

 occasional occurrence of two separate carpalia (i and 5) among Cetacea is secondary ; 

 the more so as we find other very considerable changes in the manus of these 

 animals || . 



To this argument might be opposed the daily increasing luunber of instances 

 brought forward in which we sec primitive characters occurring precisely in those 

 species, or in those organs, which in other respects are highly differentiated (specialized), 

 the preservation of old characters l)eing obviously due to the specialization of others. 

 This by no means new truth was, if I am not mistaken, first enunciated by Haeckel. 



In support of the foregoing, I wish to refer to a very noteworthy remark by Gegenbaur 

 liimself. In defence of certain conclusions arrived at in his well-known " Gliedmaassen- 

 skeiet der Enaliosaurier " ^, he states that in Sauropterygia and Ichthyopterygia the 



* System d. very;!. Aiiat. ii. 2, pp. 3iJ3, :^94 (181^5). t ' Anatomy of Vertebrates,' ii. p. 390 (18G6). 



X ' A Monog-raph of the Insectivora,' p. 21 (1S82). § Areh. de Biologie, v. p. 84 (1884). 



II " Die Eiiiheitlicbkoit des lIuiiKitmn der Siiiigethiere ist voii mir al.s ein auf dem Wcge der Thylogenese 

 erworbener Befund erklart wordeii, da in niederen .Vbtbeilungen der vierto und fiinfte Finger je ein discretes 

 Oarpalstuck besitzen. Da jcner Erwerb durch Concrescenz bald auf die Siiugetbiero libcrging, moobte ich bezweifeln, 

 dass ira Carpus der Cetaceen der uicdere Zustand nocli zu erwcisen ist, selbst weim auoh unter den vielerlei dort 

 bestehendcn Befundeu ein Carpale 4 und ein C'ar[)ale 5 sicb darstellt. Denn die iibrigon Veninderungen sind in 

 diescm Handabscbuitto zu bedeutend, als dass eiu seamtUh- crfolgtes Zustandekommen eiues dem uraprungiieben 

 ahnlicben Vcrhalteus zweier distaler Car[)alia ausgeschlossen ware."' (C. Gegenbaur, Vergl. Anat. der Wirbelthiere, 

 i. p. 542, 1898). 



^ Jen. Zeitschr. v. (1870). 



