

















50 



ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



condyles is relatively wider than in the Camel, and the process above the inner 

 condyle is more angular ; in both these respects the Macrauchene inclines towards 



the Palaeothere. 



Macrauch 



same transitional character which is afforded by the definable limits of the anchy- 

 losed bones of the fore-arm. In the Pachyderma the fibula is an entire and dis- 

 tinct bone. In the Ruminantia, with the exception of the small Musk-deer, and, 

 in an inferior degree, the Elk, the fibula appears only as a short continuous process 

 sent down from the under part of the external condyle of the tibia. In the 

 Camel tribe the only trace of the fibula in the bones of the leg, is this process in 



a still more rudimental state. 



Macrauch 



fluent with the tibia through nearly its whole extent : the proximal part of the 

 fibula is well defined ; its head is anchylosed to the outer condyle of the tibia, but 

 the shaft is continued free for the extent of nearly two inches, and then again 

 becomes confluent with the tibia, forming apparently the outer ridge of that bone. 

 About five inches from the distal end of the tibia this outer ridge becomes flat- 

 tened by being, as it were, pressed against the tibia, and the anterior and pos- 

 terior edges are raised above the level of the tibia ; beyond this part the limits 

 of the fibula begin again to be defined by deep vascular grooves. The outer side 

 of the distal end of the fibula is excavated by a broad tendinous groove. The 

 fibula and tibia are distinct bones in both the Palaeothere and Anoplothere, as in 

 the Pachyderms. It is to the former genus, however, especially Pal. magnum, that 

 the Macrauchene presents the nearest approach in the general form of the tibia, 

 the principal bone of its leg : but in the Macrauchene the tibia is relatively 

 shorter, and thicker, and is straighter and less expanded at its extremities, 

 especially the upper one, than in any of the Palaeotheres. 



The mesial boundaries of the two superior articulating surfaces of the tibia 

 are raised in the form of ridges, which are separated by a deep groove ; of these 

 ridges the external is the highest, as in Pal. magnum: but the articular surfaces 

 in the Macrauchene slope away from these ridges more than in the Palaeotheres. 

 The rotular or anterior tuberosity of the tibia is more produced, and rises higher 

 than in the Palaeotheres ; the ridge continued downwards from this process is 

 more marked in the Macrauchene, and its limits are better defined : the shaft of 

 the tibia below the ridge is also more flattened in the antero-posterior direction 

 than in the Palaeothere. The configuration of the back part of both proximal and 

 distal extremities of the tibia are so clearly and accurately given in figures 2 and 

 3, PL XIII., as to render verbal description unnecessary. Neither the text nor 

 the figures in the i Ossemens Fossiles' afford the means of pursuing the comparison 

 between the Macrauchene and Palaeothere in these particulars ; and I proceed, 





