FIGS. 5 and 6. Two specimens of the atlas in which there is incomplete dorsal arch formation. Fig. 5, specimen No. 258637 F2, 



U. S. National Museum. Fig. 6, specimen No. 262993, U. S. National Museum. 



FIG. 7. Specimen showing symmetry of the dorsal laminae. Specimen No. 256457, U. S. National Museum. 

 FIG. 8. Specimen showing asymmetry of the dorsal laminae. Specimen No. 271782, U. S. National Museum. 

 FIG. 9. Posterior view of the cervical vertebrae, of which the fifth lacks dorsal laminae. Specimen No. 227471, U. S. Nat. Mus. 

 FIG. 10. Specimen showing open sacral canal and partial sacralization of fifth lumbar vertebra, the dorsal arch of which is bifid. 



X 0.7. Specimen No. 17980506, U. S. National Museum. 

 FIG. 11. Specimen showing fusion of atlas and occiput, the posterior arch of the atlas being incomplete. 



