SHUFELDT : OSTEOLOGY OF THE STEGANOPODES 155 



from the centrum upon either side. This traverses the entire length of the verte- 

 bral body in the third, fourth, fifth, sixth, and seventh vertebne, but becomes less 

 and less marked. On the eighth it is strong again, running between the enor- 

 mously long parapophysial processes. In the ninth it is the subvertebral arterial 

 channel, and is arched over with bone anteriorly. This remains to be the case to 

 the thirteenth inclusive, while in the fourteenth the channel disappears behind, 

 though the covered arterial passage still persists on the antero-ventral aspect, beneath 

 the centrum. Both are absent in the fifteenth vertebra. Parial parapophysial spines 

 first appear in the axis, where their distal apices fuse with the bone posteriorly. 

 These spines, though present, are by no means a prominent character in the third to 

 the seventh vertebra inclusive. Suddenly in the eighth they become remarkably 

 developed, and are nearly as long as the bone itself. In the ninth they at once 

 commence to shorten again, and this rapidly continues to be the case, until they, 

 after somewhat changing their character, have entirely disappeared in the seven- 

 teenth vertebra. A most remarkable series of "lateral canals" exist in these 

 vertebrae. I note them first in the axis, where they are of capillary dimensions 

 and run nearly the entire length of that elongated bone. Anteriorly, either one 

 opens at the base of the odontoid process, the posterior opening being on the side 

 of the vertebra near the postzygapophysial base. In the third vertebra these canals 

 are almost imperceptibly increased in caliber, and open upon either side, anteriorly, 

 in a slit which is seen to exist between the prezygapophysial facet and the very 

 much vertically compressed facet of the centrum. Behind, it opens a couple of 

 millimeters in front of the articular surface of the centrum. But little change 

 takes place in this particular in the fourth to the seventh vertebra inclusive, except 

 that in the fifth, sixth and seventh a minute foraminal opening pierces the canal on 

 either side about the middle of the bone on its ventral aspect. In the eighth 

 vertebra the caliber of the lateral canals is about doubled and their posterior open- 

 ings are moved far forwards so as to be found on the side of the vertebra, above the 

 base of the enormously elongated parapophysial process ; and between two fringe- 

 like, long, ossified tendons that are attached to and especially characterize this 

 bone of the vertebral chain. With their anterior openings remaining practically 

 the same as described above, and the hinder ones just posterior to the parapophyses, 

 no change is noted in the ninth except an increase in point of the size of the tube 

 on either side. This increase goes on gradually to include the eighteenth vertebra, 

 in which bone these lateral canals last appear. In the seventeenth they are very 

 short, truly lateral, and somewhat compressed from above downwards ; markedly 

 most compressed in the eighteenth. 



