48 



ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



) 



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



metacarpals. 



The articulation at the distal extremity of the proximal phalanges (fig. 5, 



PL XI.) is simple, and not divided into two pulleys by a longitudinal ridge; 



it is slightly concave from side to side ; but in its extent upon the anterior and 



posterior surfaces of the bone indicates a freedom of flexion and extension of the 



toes, which harmonizes with the structure of the joint above. 



The proximal articulating surfaces of the second phalanges (fig. 7, PL XI. 

 corresponds of course to those to which they are adapted ; they are, however, 

 characterized by sending upwards an obtuse process from the middle of their 

 anterior margin. The distal articulating surfaces (fig. 8, PL XI.) resemble those 

 of the proximal phalanges, but extend further upon the back part of the phalanx 

 than the front, indicating the more horizontal position of the second phalanges. 



The last phalanx, does not resemble the neatly defined ungulate phalanges 

 of the Ruminantia, and Solipedia, but has the irregular form characteristic of those 

 of the Pachydermata. 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, (figs. 7 and 9, 

 PL XI.) A portion of this phalanx extends backwards behind the articular 

 surface, as in the corresponding bone of the Palseothere and Rhinoceros. 



The femur of the Macrauchenia (fig. 1, PL XII.) is full two feet in length, 

 and consequently longer than in 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 extremities 

 as compared with the diameter of the shaft, it more resembles that of the Camel. 

 The femur of the Giraffe deviates from that of the Macrauchenia in the excessive 

 expansion of its distal extremity. But the most striking evidence deducible 

 from this bone, of the affinity of the Macrauchenia to the true Pachydermatous 

 type is afforded by the evident traces of a third trochanter, the outline of which 

 is conjecturally restored in the figure. Of the Pachyderms which have this cha- 

 racteristic structure, the extinct Palseothere offers the nearest resemblance to 

 the Macrauchene in the general form and structure of the femur. 



The head of the femur in the Macrauchene (fig. 2, PL XII.) presents the 

 form of a pretty regular hemisphere ; it is less flattened above, and is directed 



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more obliquely inwards than in the Palseothere : the neck supporting it does not 

 project so far from the shaft as in the Palseothere or Tapir, but farther than 

 in the Camel. The great trochanter rises above the level of the head ; in which 

 structure and in the depression between the head and trochanter, the femur of 

 the Macrauchene offers a character intermediate between the Tapir or Palseo- 

 there, and the Camel. The lesser trochanter is a slight projection from a ridge 



