MEKTJIAM: TRTASRIC ICHTII YOS.U'RTA. 



43 



Fig. 48. IHi Hi i/iix/iii rux intcrmedius Conylx-arc. Caudal series, X ')' 1(i . (Adapted from Owen.) 



Fig. 49. Ichthyosaurus quadriscissus Quenstedt. Caudal series, about 



(After Fraas.) 



natural size. 



is a continuous series of over fifty vertebrae showing the structure of the 

 greater portion of the caudal region. At the thirty-fifth centrum in this 

 series, which appears to represent a point normally thirty-five to forty centra 

 behind the pelvis, a bend occurs in the tail. At this point the neural spines sud- 

 denly stand erect instead of inclining backward, and behind the thirty-fifth 



Fig. 50. Outline of the vertebral column of Mixosaurus. From rough sketch by the author. 



vertebra as far as the fifty-sixth they are inclined forward. The spines are not 

 greatly elongated as in Mixosaurus. but keep a more nearly even height through 

 the tail. At the thirty-fifth vertebra a change also occurs in the centra, 

 which are considerably shortened inferiorly, indicating vertical curvature, and 

 the diapophyses suddenly disappear. For some distance behind the thirty- 

 fifth vertebra the centra increase somewhat in height and at the same time 

 become absolutely narrower transversely. Small Y-shaped chevrons are pres- 

 ent to the end of the series. 



