GILMORE: OSTEOLOGY OF BAPTANODON (MARSH) 107 
The evidence to which I have had access is not conclusive but it has suggested 
to me that in Baptanodon this is not a union of the two but a development of the 
parapophyses with a consequent reduction and final passing away of the diapophyses. 
(Compare 1, 2, 3, 4, fig. 18.) It will be noticed in the cervical (1) region that the 
diapophyses presents the more robust articular surface of the two; the anterior dorsal 
(2) shows the two facets nearly equal; the median dorsal (3) indicates an increase 
in size of the parapophysis with a corresponding decrease of the diapophysis. It 
will be observed that in all three regions the distance between the facets remains 
about constant. 
In the Triassic genus Shastasawrus Dr. Merriam has shown that the parapophyses 
become obsolete in the anterior dorsal region with a consequent increase in the size 
of the diapophyses. 
The single process in Baptanodon gradually decreases in size posteriorly and 
finally fades away at some point in the caudal region as is shown by fig. 19. Owen 
has shown that this single process in J. communis disappears on the eightieth vertebra 
and it is at this point that the downward bend or depression of the tail takes place. 
Professor Knight has added some important information to our 
knowledge of the tail of the American form as follows: ‘In speci- 
men ‘TT’ in the same collection (University of Wyoming) there are 
forty-six consecutive caudal vertebrae. ‘These are of the usual ichthy- Fig. 19. 1 
osaurian type and represent an animal that had an extremely long and 3"¢ 2 end and 
lateral views of 
slender tail. The reduction in the size of the vertebree occurs very an extreme cau- 
near the body and within a distance of a few inches, the vertebree dal of Baptano- 
don discus. (No. 
603). One half 
reduction have reduced margins,” in fact in two of them the artic- natural size. ne, 
decrease in diameter over one half. The vertebree in the area of 
ulation nearly meets upon the side of the centrum. * * * Although ln! 
caudal vertebree from at least a half dozen different animals have been examined, 
no trace of chevrons has been observed, and the vertebree lack chevron facets.” 
On the anterior vertebrze the neural arches are held together by well developed 
zygapophyses. The anterior arches have paired zygapophysial facets which unite 
to form a single median one at some point between the sixth and ninth cervicals. 
This information is derived from the cervical region of No. 878. The zygapophysial 
facets have their surfaces roughened indicating as shown previously by Dr. Merriam 
in the genus Shastasaurus, the presence of considerable cartilage. 
A number of the anterior cervicals of No. 878 (see Pl. VII.) have the arches and 
39 It occurs to me that these vertepre with reduced margins may represent the point of divergence of the vertebral 
column into the lower lobe of the candal fin. 
