56 



Field Columbian Museum — Geoloqy, Vol. II. 



sutures separating the angular, surangular and dentary are shown in 

 the figure. 



Cervical Vertebra. — There were twenty-eight cervical vertebrae 

 in a continuous series preserved, the last five or six, owing to 

 exposure, in a less perfect condition: the others complete or nearly 

 so. Traces of the sutures uniting the neural arches with the centra 

 can be observed in the third and fourth vertebrae only. The atlas and 

 axis are so wedged in the compressed occipital region that the former 

 bone can not be distinguished, and the latter is visible in part only. 

 The third vertebrae, herewith figured, differs from the following ones 

 in the greater obliquity of the spine, in the more oblique anterior 

 face of the centrum, in the presence of a conspicuous carina below in 

 front, and in the simple, pointed shape of the single-headed rib. The 

 fourth vertebrae has the neural process less oblique and broader, the 

 carina in the middle of the concavity of the under surface not visible 

 from the side; the rib is broad and of nearly equal width throughout. 

 In the sixth vertebrae and beyond the neural process is broader and 

 nearly vertical; the ribs are broad, with more marked anterior and 

 posterior prolongations distally. The spines increase in width through- 

 out the series, but are only a little longer posteriorly. The posterior 

 centrum is more than three times the length of the anterior ones and 

 the diameter posteriorly is more than twice that anteriorly. The ribs 

 of the posterior vertebrae are but little longer, though much wider, 

 than those of the anterior vertebrae. The following measurements 

 will exhibit these differences in size more exactly: 



