1899.] XHE CABPUS OF CTEIfOMYS. 435 



position corresponds perfectly with one which in other Marsupials 

 (e.g. Petaurus and Trichosurus) is perfectly distinct and is interpreted 

 as lunatum (intermedium)." ^ In the stages figured on plate 33 

 (figs. 5 & 6) the element of Phascolarctus is not entirely independent, 

 "sondern bereits dem Radius angewachsen. — In welter ausge- 

 bildeten Stadien finde ich keine Spur von einem solchen Element 

 mehr, aber der Radius besitzt an der entsprechenden Stelle einen 

 mehr oder weniger deutlichen Vorsprung, den ich als dessen 

 Homologon betracbten mochte." Now, not only the position of 

 this element of Phascolarctus, but also what Emery states about its 

 subsequent fusion with the radius, correspond so exactly with what 

 I find in the above-named Rodents, that both appear to be homo- 

 logous. The so-called scapho-luuar of Gtenomi/s, Mus, Bruchyuromys, 

 &c. would then at first sight seem to be a greatly enlarged scaphoid, 

 which has overtaken the functions of the lunar, the latter having 

 become reduced and eventually fused with the radius. 



Whenever we find in the carpus or tarsus of a species or whole 

 group a large bone occupying the same place as tw^o smaller bones 

 in another, the conclusion nearest at hand is that the single bone 

 is the result of the fusion of two originally distinct ossicles. But 

 this inference is by no means always valid. I have elsewhere 

 undertaken to demonstrate that the hamatum of Mammalia is 

 not a compound of carpale 4 and carpale 5, but is carpale 4 only ; 

 for the obvious reason that there is a carpale 5, which however is 

 generally cut away in the skeletons, being considered as a despicable 

 sesamoid. In other instances it either vanishes or becomes fused 

 with the tuberosity of the fifth metacarpal ; it fuses with carpale 4 

 only in the case of a few Cetacea. 



I will here give another remarkable instance of a similar kind. 

 In the small Rodent group Bathyerginae, the genera Batliyergus 

 and Qeorychus {capensis) exhibit in their carpus a distinct ossicle, 

 which from its position we call centrale ; proximad it articulates 

 chiefly with the equally distinct lunatum, and distad with the third 

 and second carpale (magnum and trapezoideum). In the closely 

 allied Myoscalops there is, occupying the place of the centrale and 

 the trapezoideum of the former two genera, only one bone, which 

 runs obliquely from the lunatum to the carpale 1 (trapezium) and, 

 on its way, articulates also with carpale 3, as does the centrale 

 of the two fore-named genera, and with the scaphoid and meta- 

 carpal II., as does the trapezoideum of Batliyergus and Georychus. 

 In the tarsus of the same genera occurs the following curious parallel. 

 In Batliyergus and Georychus the navicular is separated fz'om the 

 second metatarsal by the tarsale 2 (mesocuneiforme): in Myoscalops 

 the navicular encroaches on the space occupied by the mesocunei- 

 forme of the former two genera and articulates with the second 

 metatarsale ; so that the mesocuneiforme seems to be missing in 

 Myoscalops. The obvious inference from this condition will 

 of course be that the single bone in the carpus of Myoscalops is a 



1 L. c. p. 373. 



