No. 397.] MOSASAURS, LIZARDS, AND SPHENODON. 7 
This history of the atlas and axis complex in the Mosasaurs, 
lizards, and Sphenodon may, in conclusion, briefly be summarized 
as follows : 
1. The intercentrum of the atlas fuses with the neural arches 
of the atlas to form the basal portion of the ring. 
2. The intercentrum of the axis fuses with the centrum of 
the axis to form a kind of hypapophysis. 
3. The intercentra of the remaining cervicals 3-7 either 
remain primitive in position, or are shifted forward upon the 
hypapophyses of the next vertebra in front. 
AMERICAN MUSEUM OF NATURAL HISTORY, 
December 7, 1899. 
