190 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



physes slightly weaker and more symmetrical. The trans- 

 verse processes are now increasing in width from before 

 backwards, and bear a slight elevation to which the 

 accessory rib is attached. 



Twelfth Yertebra (figs. 12 and 18). — Strengthening 

 ridges as in 11. Asymmetry slight. Post-zygapophyses 

 faint and practically symmetrical. Transverse process 

 proximally very wide from before backwards. Neural 

 spine more consolidated, bnt still consists of 2 bony tubes 

 placed side by side. 



Thirteenth Yertebra (fig. 18). — Three strengthening 

 ridges on eyeless side, and two on centrum and one on 

 transverse process on ocular side. Symmetry as in 12. 

 Transverse processes only very slightly asymmetrical. 

 Accessory rib rudimentary and attached to a prominent 

 elevation near base of transverse process (A.R. 13 ). Last 

 vertebra to bear free ribs of either series. Behind the 

 transverse processes and true ribs are converted into the 

 haemal arch and spine. This gradual conversion, and the 

 homology of the parts, is well shown in figure 18. Zygapo- 

 physes as in 12. Transverse processes very wide from 

 before backwards. 



Fourteenth Yertebra (figs. 13 and 18).— The first 

 caudal vertebra. Three strengthening ridges on each 

 side. The neural and haemal spines are the longest of 

 any, and both incline slightly backwards and towards the 

 eyeless side. The neural spine, which is only about two- 

 thirds the length of the haemal spine, is somewhat com- 

 plex, and contains three longitudinal cavities, all of which 

 open posteriorly at the top of the spine. The left anterior 

 zygapophysis is much more prominent than the right, 

 whilst the post-zygapophyses are feeble and no longer 

 obvious as projections from the posterior border of the 

 neural arch. The posterior notochordal space, unlike 



