44 



ZOOLOGY OF THE YOYAGE OF THE BEAGLE. 



ever, the contour of the superior costa is broken by a deep round notch immediately 

 behind the coracoid : in the Hippopotamus this process arches in a slight degree 

 backward over a corresponding but wider and shallower notch. In the Palceo- 

 therium crassum the concavity of the superior costa, behind the coracoid, is as 

 slight as in the Rhinoceros ; but in the Macrauchenia the superior costa of the 

 scapula begins to rise or stretch away from the parallel of the spine, immediately 

 behind the coracoid process. The modifications of the spine of the scapula which 

 characterize respectively the Ruminants and Pachyderms have been clearly and 

 concisely set forth by Cuvier, who at the same time points out the exceptional 

 condition which the Camelidce present in the production of the acromial angle. 

 It was with peculiar interest and care, therefore, that I reunited all the fragments 

 of the scapula of the Macrauchene, in the hope of gaining from this part of the 

 skeleton as decisive evidence of an affinity to the Camel as the cervical vertebrae 

 had afforded. It unfortunately happens, however, that the part of the scapula 

 most important in this comparison is broken off; yet from this very circumstance, 

 combined with a slight inclination forwards of the anterior margin of the spine 

 immediately beneath the fractured acromion, and from the thickness of the frac- 

 tured surface, we may infer that the acromial angle of the spine was more produced 

 than in the ordinary Ruminants, although evidently in a less degree than in the 



Camel tribe. 



Macraucher 



and equals the Pachyderms in the elevation and extent of its scapular spine : 

 but this process commences about half an inch behind the glenoid cavity, and 

 rises at once to the height of three inches above the plane of the scapula; in 

 which structure we may trace the same tendency to the Ruminant type, as is 

 manifested in the scapula of the Hippopotamus and Anoplotherium ; for in most 

 other Pachyderms the spine increases gradually from its extremities to the 

 middle part. The anterior margin of the spine beneath the short acromion is 

 perforated by an elliptical fissure measuring ten lines, by three lines. The extent 

 of the spine which is preserved, measures eight inches and a half; it is a thin 

 and nearly straight plate of bone, expanding into a thick and rugged upper 

 margin, which slightly over-arches the inferior fossa, (fig. 1, PI. IX.) In its 

 general form and proportions the spine of the scapula in Macrauchenia presents 

 the nearest resemblance to that of the Hippopotamus ; but its origin is closer to 

 the articular surface of the scapula than in this, or any other Pachyderm al or 



Ruminant genus. 



The portion of the antibrachium of the Macrauchenia which is preserved, 



presents a condition of the radius and ulna intermediate to those which respec- 

 tively characterize the same bones in the Pachyderms and Camels. In the 

 former the radius and ulna are separate bones, united in the prone position by 

 ligament, yet so that the movement of supination cannot be performed ; in the 



