604 E. B. BRANSON 



supposed. 1 The arch is small and bears no rib. The axis is com- 

 posed of the same elements as the atlas, with possibly small pleuro- 

 centra in addition, but its arch is larger and bears a small rib. The 

 rib seems not to have been attached to the intercentrum. The third 

 cervical has small pleurocentra which support the arch. Posterior 

 to the third the pleurocentra increase in size and push the intercentra 

 far apart below. Toward the sacrum they again decrease in size 

 and are pushed upward, finally resting on the intercentrum of the 

 vertebra behind. The pleurocentra of the anterior caudals are 

 reduced in size, and they gradually decrease caudad, until those of 

 the distal caudals are very small. In the thoracic region the pleuro- 

 centra support the arch, but, as they become more and more reduced 

 in size, the support is shifted more and more to the intercentrum, until 

 in the caudals the latter forms the principal support. The intercentra 

 are enlarged in the sacral and caudal regions, and those of the sacrum 

 are opposed below. 



The specimens that furnish these new facts are the ones from 

 which Dr. Baur drew his conclusions, published in the November 

 number of the American Naturalist of 1897. But Dr. Baur saw 

 only three or four vertebrae free from the matrix. They were from 

 the thoracic region, and his statements concerning them are accurate. 

 The atlas was free from the matrix only on one side, and he says of 

 it: "Only the first intercentrum is connected with the neural arches 

 of the first vertebra, the atlas forming the atlas ring as in all Amniota." 2 

 The matrix still covered the vertebrae behind the atlas when the writer 

 began work on them, and it was not then apparent that the second 

 vertebra, like the first, has no pleurocentra in that specimen. 



In the specimen figured by Cope the axis has no pleurocentra; 

 "but he does not mention this peculiarity in his description. 3 The 

 intercentrum of the atlas was missing, and it was natural to suppose 

 that the pleurocentra of both atlas and axis had been lost with it. 

 But reference to his figure shows that there is little space for pleuro- 

 centra between the third intercentrum and the diapophysis of the 

 axis arch. After examining Cope's specimen, the writer is not fully 



1 Proceedings of the American Philosophical Society, 1880, Vol. XIX, pp. 52, 56. 



2 American Naturalist, 1897, p. 978. 



3 Proceedings of the American Philosophical Society, Vol. XIX, Plate III, Fig. 5. 



