46 
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 Vertebra (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, but still consists of 2 bony tubes 
placed side by side. 
Thirteenth Vertebra (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.#.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 Vertebra (figs. 13 and 18)—tThe 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. he 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 
