SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. I23 



rior portion is bent downward, making the broad side present laterally, 

 somewhat as in the camel. This anterior portion is connected with the 

 centrum by a comparatively narrow neck and becomes much broader 

 antero-posteriorly on the ventral side. The hinder portion of the process 

 is much more extended from before backward than the forward portion, is 

 horizontal in direction and has a more elevated position, arising from the 

 centrum a little below the base of the neural arch. 



In Macraucheiiia, this vertebra has a broader, heavier and more depressed 

 centrum than in Theosodon, with faintly marked ventral keel, which does 

 not divide into divergent ridges. The anterior portion of the transverse 

 process is shorter from before backward, not projecting so far in front of 

 the centrum, has a much more thickened and rugose free border, and is 

 not constricted at the junction with the centrum. 



In Theosodon, the fifth cervical (PI. XVIII, figs. 4, /i^d) differs so little 

 from the fourth as hardly to require a separate description. It is large and 

 heavy, has a neural spine which is low and shorter from before backward 

 and the anterior portion of the transverse process joins the centrum by its 

 full breadth, without constriction. 



The sixth cervical is much shorter than any of the preceding vertebrae, 

 except the atlas, and the centrum is so curved that the ventral face is con- 

 cave antero-posteriorly, and has a very low and thin, but very distinct 

 median keel. The broad neural arch encloses quite a large neural canal, 

 and the spine has a forward inclination. The transverse processes are, as 

 usual in the Mammalia, divided into diapophysial and pleurapophysial 

 elements ; the former is a short, broad plate, extending horizontally out- 

 ward from the sides of the centrum, with thick and rugose free border, 

 and, as in mammals generally, is perforated by the canal for the vertebral 

 artery. The pleurapophysis, or inferior lamella, is very large and promi- 

 nent, extends along the whole length of the centrum and is directed almost 

 downward, with thickened ventral border. 



In Macrauchenia, this vertebra is of a similar type to that just described, 

 but differs in a number of details. ( i ) The centrum is considerably shorter 

 in proportion to the length of the fourth cervical, as well as broader and 

 more depressed. (2) The neural canal is smaller and the zygapophyses, 

 especially the posterior pair, are much more strongly divergent from each 

 other. (3) The diapophysis is thicker dorso-ventrally and is not perforated 

 by the vertebrarterial canal, while the inferior lamella is less prominent 



