106 MEMOIRS OF THE CARNEGIE MUSEUM 
From the cervicals back through the dors sal region the breadth remains greater 
than the height but the shield-shaped form of the cervical centra gradually changes 
to what has been called “pear shaped” (see figs. 16 and 17), in the regions here 
(2 
Fic. 16. Cross-section of a dorsal centrum of Baptanodon discus (No. 603). One half natural size. d, diapophysis ; 
p, parapophysis ; z, neurapophysial surface. 
Fic. 17. Cross-section of posterior dorsal or anterior caudal centrum of Baptanodon discus (No. 603). One half 
natural size. jp, (?) parapophysis; x, neurapophysial surface. 
considered as middle and posterior dorsals, and this form gradually assumes the 
compressed elliptical contour seen in the caudals (see fig. 19). 
The change in form of the centra brings a corresponding transition of the dia- 
and parapophyses. These processes gradually move down the side of the centra, 
until finally only one oblique process remains on the extreme lower side of the 
centrum. ‘This type probably represents the posterior dorsal region (see fig. 17). 
Fic. 18. Lateral view of centra from different regions of Baptanodon discus (No. 603). One half natural size. 1, 
anterior cervical ; 2, anterior dorsal; 3, dorsal; 4, posterior dorsal or anterior caudal; d, diapophysis ; p, para- 
pophysis. ‘ 
In Ichthyosawrus Owen described the reduction to a single facet as a union of 
the two ’pophyses. He thought the diapophysis dropped more rapidly than the 
parapophysis, thus meeting the latter with which it united to form the single oblique 
process. 
