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But the femur of Macrauchenia, in the flatness of the back part of 

 its neck, and the elongated form of the post-trochanterian depression, 

 resembles that of the Camel rather than that of the Palaeothere ; and the 

 same resemblance is shown in the cylindrical figure, straightness and 

 length of the shaft. The depth of the trochanterian depression, and the 

 incurvation of the strong ridge continued downwards from the great 

 trochanter, are individual peculiarities in the Macrauchenia. 



In the general form and relative size of the condyles of the distal extre- 

 mity of the femur, the Macrauchene is intermediate between the Camel and 

 Palaeothere, but more resembles the latter. In the articular surface for 

 the patella it deviates somewhat from the Palaeothere, having this part 

 longer in proportion to its breadth, more regularly and deeply concave 

 from side to side, and with its lateral boundaries more sharply defined. 



948. The proximal extremities of the anchylosed tibia and fibula of the 

 right leg of the Macrauchenia patachonica. 



From the tertiary deposits of Port St. Julian, Patagonia. 



Presented by Charles Darwin, Esq., F.R.&. 



949. The distal anchylosed extremities of the same tibia and fibula. 



Presented by Charles Darwin, Esq., F.R.S. 



In the structure of the bones of the leg of the Macrauchenia we find 

 the same transitional character between the Pachydermal and Ruminant 

 types which is afforded by the definable limits of the anchylosed bones of 

 the fore-arm. In the Pachyderms the fibula is an entire and distinct 

 bone : in the Ruminants, with the exception of the small Musk Deer, 

 and in an inferior degree the Elk, the fibula appears only as a short con- 

 tinuous process sent down from the under part of the external condyle of 

 the tibia, its distal end being represented by a detached ossicle : in the 

 Camel tribe the proximal process is in a still more rudimental state. In 

 the Macrauchenia the fibulais entire, but is confluent 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. 



2g2 



