42 



ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



(fig. 4, PL VIII.) have concave articular facets turned towards, and nearly con- 

 tinued into, each other at their lower extremities ; so as to " 



form together a 



deep semilunar notch, into which the corresponding convex articular surfaces 

 of the posterior oblique processes of the adjoining vertebra (fig. 3, PL VIII.) are 

 firmly locked. In the close approximation of the two anterior concave articular 

 facets, which are separated from each other only by a vertical ridge, and a 

 rough surface of about three or four lines in breadth, the lumbar vertebrae 



of the Horse, and differ from those of 



inches. When 



of the Macrauchene resemble those 

 the Camel-tribe and Ruminants generally, in which those surfaces are wider 

 apart. In the hook-like form, however, of these articular processes the lumbar 

 vertebra? of the Macrauchene differ from those of the Horse; and resemble 

 those of many Ruminant species, and of the Anoplothere ;* but the degree 

 of concavity of the articulating surface is not so great in the Macrauchene. It 

 would be interesting to determine the relations which the lumbar vertebra? of the 

 Macrauchene bear to those of the Palaeothere ; but the indication which Cuvier 

 gives of the single lumbar vertebra, of which he had cognizance in the latter 

 >enust is too slight to enable me to enter upon the comparison. 



The whole length of the lumbar region in the Macrauchene is twenty 



the bodies of these vertebra? are naturally adapted together, 

 they form a slight curve, indicating that the loins of the Macrauchene were 

 arched, or bent downwards towards the sacrum. That the lumbar vertebra? 

 were rigidly connected together, or but slightly flexible, is evident from the 

 flatness of the articular surfaces of the vertebral body, and by the circum- 

 stance of ossification having extended along the anterior vertebral ligaments, 

 and produced an anchylosis between the fourth and fifth lumbar vertebra?; 

 (fig. 2, c, PI. VIII.) This kind of ossification is frequent in aged horses, and 

 I have seen an example of a similar anchylosis of the lumbar vertebra?, by 

 abnormal deposition of bone in their anterior ligaments, in the skeleton of a 

 Hippopotamus preserved in the Senkenbergian Museum, at Frankfort. 



In preparing the preceding account of the cervical and lumbar regions of 

 the vertebral column of the Macrauchene, I have felt frequently a strong desire 

 to enter into a comparison between them and the corresponding vertebra? of the 

 extinct Pachyderms of the Paris Basin. Some of these, as the Jnoplotherinm 

 gracile, in the length and slenderness of the cervical vertebra?, resemble both 

 Auchenia and Macrauchenia; others, as the Palceotherium minus, and probably the 

 rest of the genus, resemble the Camelidce and Macrauchenia in having seven 

 lumbar vertebra?. Cuvier points out the resemblance which the atlas of the 

 Anonlnthprp. hears to that of the Camel, and especially of the Llama ;t but he 



* Cuvier, Ossemens Fossiles, iii. p. 238. 



t Loc. cit. p. 234. 



t Loc. cit. p. 235 



