226 



structure of the metacarpo- phalangeal joints in the Hog falls far short of 

 the compactness and strength, combined with freedom of flexion and ex- 

 tension, which distinguish those of the Macrauchenia : the Palcsotherium 

 medium, Cuv., most resembles the Macrauchenia in the structure of the 

 trochlear metacarpo-phalangeal joints ; but both in this species and the 

 Palceotherium crassum^the articular surface at the distal end of the meta- 

 carpal bone is relatively narrower than in the Macrauchenia : moreover, 

 all the species of the extinct Palaeothere differ from the Macrauchenia in 

 the greater size and strength of the middle as compared with the lateral 

 metacarpal bones. The last phalanx does not resemble the neatly de- 

 fined ungulate phalanges of the Ruminantia and Solipeda, but has the 

 irregular form characteristic of those of the Pachyderma ; it is wedge- 

 shaped, broader than it is long, with a rugged surface, except where it 

 plays upon the distal end of the second phalanx, where it is slightly 

 concave in one direction and convex in the other. A portion of this 

 phalanx extends backwards behind the articular surface as in the corre- 

 sponding bone of the Palaeothere and Rhinoceros. 



947. The right femur of the Macrauchenia patachonica. 



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



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



This fine bone is full two feet in length, and consequently longer than 

 the femur of any known Camel or Rhinoceros ; as compared with its 

 transverse diameter it is much longer than the femur of the latter animal : 

 in the proportion of its breadth to its length and the expansion of its ex- 

 tremities as compared with the diameter of the shaft, it more resembles 

 that of the Camel. The femur of the Giraffe differs from that of the 

 Macrauchenia in the excessive expansion of its distal extremity. But 

 the most striking evidence which the present femur affords of the 

 affinity of the Macrauchenia to the anisodactyle modification of the 

 Pachydermal type, is the presence of a third trochanter. Of the Pachy- 

 derms which have this characteristic structure, the extinct Palaeothere 

 offers the nearest resemblance to the Macrauchenia in the general form 

 and structure of the femur. 



