CAUDAL VERTEBRA OF HESPERORXIS. 79 



The Second Caudal Veetebea. (Plate XII, figure 2.) 



The second free caudal vertebra is much shorter than the preceding, 

 and its centrum is much more massive. The anterior articular face is 

 somewhat convex, and has a depressed sub-circular outline, with the lower 

 half of the margin excavated. The posterior articular face is nearly flat, 

 but somewhat concave near the centre. 



The transverse processes are directed outward and slightly downward, 

 terminating - a little below the ventral surface of the centrum. They are 

 longer than those of the preceding vertebra, but have less antero-posterior 

 extent. 



The neural spine is stout and elevated, and has its superior extremity 

 expanded into a round knob. The neural canal is large, and vertically 

 oval in outline, and its lower margin cuts into the upper border of the 

 anterior articular face. The posterior margin of the neiual arch, when 

 seen from the side, is parallel with that of the posterior articular face of 

 the centrum, and slightly in advance of it. 



Measurements of Second Caudal Vertebra. (No. 1206.) 



Length of centrum, . 15.0 mm 



Transverse diameter of anterior articulation, 14.0 



Vertical diameter of anterior articulation, 10.0 



Transverse diameter of posterior articulation, 13.0 



Vertical diameter of posterior articulation, . 11.0 



Diameter of vertebra, across transverse processes, 29.0 



Length of transverse processes from centrum, 8.0 



Length of floor of neural canal, 12.0 



Vertical diameter of anterior opening of neural canal, 5.0 



Vertical diameter of posterior opening of neural canal, T.O 



Height of neural spine above centrum, 21.0 



The Third Caudal Vertebra. (Plate XII, figure 3.) 



The third caudal vertebra of Hesperomis regalis, or the fortieth in the 

 column, is the shortest of the series, with the exception of those at the end 

 of the tail. It is also the first caudal which is entirely behind the ends of 

 the ilia, and its shortness is probably due to the fact that here the flexure 

 of the tail essentially began. 



