24 MEMOIRS OF THE CARNEGIE MUSEUM 



much constricted medially and expanded at their extremities. The zygapophyses 

 are broad, with the articular surfaces transversely expanded, but contracted antero- 

 posteriorly. The cervical rib is long and lies below the inferior border of the cen- 

 trum. The combined length of the anterior and posterior costal processes are but 

 little less than that of the centrum. The apices of the neural spines are both want- 

 ing in this vertebra. They have been restored as rather low and broad superiorly. 

 In Fig. 7 are shown comparative views of this vertebra and cervicals 10 and 1 2, which 

 immediately precede and succeed it. 



The Twelfth Cervical. — This does not materially differ from the succeeding cer- 

 vicals, but when seen from the side it contrasts strikingly with C. 11, as see Fig. 7, 

 and PL III. There is no vertebrarterial canal. The bottom of the pleuro-central 

 cavity is less complicated. It is invaded by four large vacuities. Three of these 

 lie posterior and one anterior to the pleuro-central lamina, which in the vertebrae of 

 this region starts from the anterior and superior border of the pleuro-central cavity 

 and extends dowuAvard and backward to the middle of the inferior border of the 

 centrum, thus dividing this cavity into an anterior and a posterior moiety. The 

 diapophysial and posterior horizontal laminae are long, occupying about two thirds 

 the total length of the centrum. The post-diapophysial cavity is open externally 

 throughout its entire length in marked contrast with the condition that obtains in 

 C. 11. There is in this vertebra a striking instance of asymmetry. On either side 

 of the neural arch and directly below the postzygapophyses there is in each of the 

 preceding and succeeding cervicals of this region a pair of large foramina about one 

 inch in diameter placed laterally and opening into the neural canal. In C. 12 this 

 foramen is present and of normal dimensions on the right side, but on the left in- 

 stead of opening into the neural canal it terminates in a shallow pit about three 

 fourths of an inch in depth and completely closed with bone at the bottom. 



The Thirteenth Cervical. — The pleuro-central cavity is more restricted posteriorly 

 than in the preceding cervicals. The pleuro-central lamina is especially prominent 

 and divides this cavity into a deep, rather small anterior and a somewhat larger 

 posterior cavity. The anterior zygapophyses are overhanging and project beyond the 

 ball of the centrum. They are each supported inferiorly, as in the other cervicals 

 of this region, by two prominent inferior blades of the prezygapophysial laminae 

 which spring from the external and superior margins of the centrum just posterior 

 to the ball and diverge to meet the zygapophyses superiorly. A third pair of 

 branches, the internal of the prezygapophysial as also of the postzygapophysial 

 laminae, converge inferiorly, meet and intersect each other just above the middle of 

 the neural canal, where they are- exceedingly thin. Below the point of intersection 



