60 SCOTT. [Vol. V. 



sinuous convolutions. The main sulci are already present in 

 Pcebrotherium, so that the brain of this genus stands to that of 

 the recent genera in the relation of embryo to adult, and affords 

 an interesting confirmation of Krueg's results obtained by 

 embryological investigation. 



IV. The Vertebral Column. 



Cope states (No. 7, p. 718) that the lumbar vertebrae of Pan- 

 tolestes have flat articular faces. 



The vertebrae of PcebrotJierium have reached a stage of devel- 

 opment which, except in a few points, is almost like that of the 

 existing forms. The neck is elongated, though decidedly shorter 

 than in the recent genera ; the transverse processes are not 

 so distinctly separated into anterior and posterior portions, and 

 on the sixth cervical the vertebrarterial canal is clearly visible. 

 The atlas has longer and more recurved transverse processes ; 

 the anterior cotyli are not notched ; there is no accessory articu- 

 lar surface on the anterior face of the inferior arch, and the 

 vertebrarterial canal has its posterior opening at the base of 

 the transverse process, not on the dorsal side of it. The axis 

 has a high, thin, plate-like neural arch, more expanded antero- 

 posteriorly, but much less massive and rugose than in the 

 modern genera ; the odontoid process is short and flattened on 

 the dorsal side, with a rounded tip. 



The dorsal vertebrae appear to number 13; they have long, 

 slender, backwardly directed spines and elongated compressed 

 centra. 



The lumbar vertebrae have depressed centra with inferior 

 median keels and lateral ridges ; the spines are thinner and 

 more compressed, and the zygapophyses show the faint begin- 

 nings of the episphenial processes which are so well developed 

 in the camel. 



The cervicals of Procamclus described and figured by Cope 

 (No. 6, p. 335, PI. LXXVIII) are intermediate between those 

 of the recent genera and those of Pazbrotherium. The atlas 

 agrees with the latter in the continuation of the transverse proc- 

 esses behind the surfaces for the axis, and with the former in 

 the position of the vertebrarterial canal, the deep emargination 

 of the outer rims of the occipital cotyli, and, apparently, in the 



