225 



942. The middle phalanx of the same toe. 



943. The distal or ungual phalanx of the same toe. 



944. The proximal phalanx of the middle toe of the Macrauchenia pata- 



chonica. 



945. The proximal phalanx of the outer toe of the Macrauchenia pata- 

 chonica. 



946. The middle phalanx of the same toe. 



The instructive portion of the right fore-foot to which the last- 

 described bones belong, presents the most important difference between the 

 extinct Macrauchenia and the Raberrant uminantia, to which it is allied in 

 the peculiar structure of the cervical vertebrae, and shows its essential affini- 

 ties to be to the tridactyle Pachyderms, as the Tapir, the Rhinoceros, and 

 more particularly to the extinct tapiroid Pachyderms of the Eocene 

 tertiary formations of Europe, called Lophiodon and Paleeotherium. 

 These bones demonstrate that the Macrauchenia had three toes on the 

 fore-feet and not more ; and that the fully developed metacarpal bones 

 are distinct, and correspond in number with the toes, and are not anchy- 

 losed into a single cannon-bone as in the Ruminants. The distal 

 articulating facet of each of the metacarpal bones extends so far upon 

 both the anterior and posterior surfaces as to describe more than a semi- 

 circle ; in the two lateral metacarpals it is traversed throughout by a 

 longitudinal convex ridge dividing it into two equal lateral parts ; the 

 ridge is most produced on the posterior half of the joint ; in the middle 

 metacarpal this ridge subsides before it reaches the anterior part of the 

 articular surface. 



The structure of the above-described joint proves that the motion of 

 the toe upon the metacarpus was much freer and more extensive than in 

 the Rhinoceros, which is the only existing ungulate mammal which pre- 

 sents the tridactyle structure in the fore-foot. In this species the 

 metacarpo-phalangeal articulations exhibit only a slight trace of the 

 longitudinal ridge and grooves which are confined to the posterior part 

 of the joint ; these are more developed in the Camelidse ; but the Hog and 

 Horse in this respect approach nearer to the Macrauchenia, though the 



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