78 ODONTORXITHES. 



The First Caudal Vertebra. (Plate XII, figure 1.) 



The first free caudal vertebra, which is the thirty-eighth in number, 

 counting from the skull, is much shorter than the preceding one in the 

 coossified sacral series, but considerably longer than those which follow. 

 In its natural position, it was entirely included between the posterior 

 extremities of the ilia. 



The anterior articular face of the centrum is vertically elliptical in 

 outline, and somewhat convex. Immediately behind this, the centrum is 

 constricted, and then expands regularly to the posterior articular face, 

 which is much larger than the one in front, and moderately concave. It is 

 sub-circular in outline, but its transverse diameter exceeds its vertical, and 

 the upper and lower margins are slightly notched on the median line. 



The transverse processes extend downward, and slightly outward, and 

 their external surfaces, which are nearly in the same plane as the sides of 

 the neural arch, were attached to the divergent iliac bones by cartilage. 



*The neural spine was elevated, and much expanded in a fore and 

 aft direction. The neural canal, at its anterior orifice, is much com- 

 pressed transversely; its posterior outlet is triangular, and very large, 

 indicating a marked expansion of the spinal cord in this region of the 

 vertebral column. This feature was doubtless directly connected with the 

 powerful movements of the tail. 



The principal dimensions of the first free caudal, or thirty-eighth 

 vertebra, in Hesperomis regalis, are given below : 



Measure?nents of First Caudal Vertebra. (No. 1206.) 



Length of centrum, 19.0 mm 



Least transverse diameter of centrum, 6.0 



Transverse diameter of anterior articulation, 6.5 



Vertical diameter of anterior articulation, 8.0 



Transverse diameter of posterior articulation, 11.0 



Vertical diameter of posterior articulation, 8.0 



Diameter of vertebra, across transverse processes, 20.0 



Extent of transverse processes below centrum, 7.0 



Length of floor of neural canal, 17.0 



Vertical diameter of anterior opening of neural canal, 4.5 



Vertical diameter of posterior opening of neural canal, - - 7.0 



