GILMORE: OSTEOLOGY OF BAPTANODON (MARSH) 105 
examination of the axis of B. marshi that the restored spine in fig. 10 is too narrow 
antero-posteriorly. 
Vertebree Posterior to the Avis. —The succeeding cervicals are very similar in their 
”? 
general form which perhaps is best described as “shield shaped.” Fig. 14 is a 
good example of the cervical centrum and the description given here may be con- 
sidered typical of the vertebree of this region. 
On the median superior surface is the smooth tract forming the basal boundary 
of the neural canal (see fig. 13) on either side separated by slight antero-posterior 
ridges are the shallow roughened neurapophysial surfaces for the attachment of 
the pads of cartilage upon which the pedicels of the neural arch rested. 
This roughened surface is placed largely on the anterior half of the cervical and 
extends outward and downward becoming confluent with the diapophysis (see fig. 
14). The parapophyses are node-like projections placed half way down and on the 
anterior margin of the centrum, being separated from the diapophyses by a concave 
longitudinal depression. The position of these two processes remains unchanged as 
far back at least as the fifteenth vertebrae, as will be seen in Pl. VII. 
The anterior vertebrae are broader than high and gradually increase in length 
posteriorly. From the splendid series of forty-one precaudal vertebre pertaining 
to the type of B. marshi, Dr. Knight has observed that the maximum length is 
reached in the nineteenth from the skull. 
Continuing back in the column (see fig. 15) it will be observed that the centra 
remain about the same height but the transverse a 
extent becomes considerably greater, also the artic- 
ular surfaces of the diapophyses which are conflu- 
ent with the neurapophysial surfaces in the cervical 
region become separated. In Ichthyosawrus this 
separation takes place on either the fourteenth or 
fifteenth vertebra. Dr. Merriam has shown that in 
one species of Shastasaurus it does not occur until 
the thirty-fifth or later. The point at which this Bie by CESSES OF ein EBENIO? 
dorsal centrum of Baptanodon discus (No. 
transition is brought about in Baptanodon cannot FUE GROEN Peelers ch Ghereorsiw 
be determined from the specimens under discus- sis; p, parapophys; x, neurapophysial 
sion, although we have evidence that they do not sutface: 
separate until the sixteenth or Jater.* (See Plate VIL.) 
38 In the Am. Jour. Sci., Vol. 50, 1895, Marsh figures a vertebra of Baptanodon natans, designated as a cervical, 
The position of the dia- and parapopbyses half way down on the side of the centrum at once shows this vertebra as 
pertaining to the region posterior to the neck. This figure was published a second time in his U. S. G. S. Monograph of 
the Vertebrate Fossils of the Denver Basin in 1897. 
