30 
TEliTrARY VEUTEERATA OF Till-] FAYOM. 
deeper, while the oval capitular facets {c.f.) are higher up and partly borne on the 
base of tlie arch, the anterior being somewhat lower than the posterior. The 
transverse ])rocesscs are larger and more massive, and each bears a well-marked 
tubercular facet {t.f.) on its outer end. The neural spine is very high and broad ; it 
slopes strongly backwards, and its anterior face is convex from side to side, while 
its posterior is deeply concave. The anterior border of the neural arch is deeply 
concave from side to side, so that in a dorsal view of the vertebra much of the neural 
surface of the centrum is exposed. At the same time the arch overhangs the 
posterior border of the centrum to a great extent. The anterior zygapophyses [a.z.) 
are mere shelf-like surfaces on the anterior border of the arch, and the posterior 
zygapophyses (jf.z.) form facets on the lower surface of the posterior border. 
In the posterior thoracic (text-fig. 18) the spine (n.sjj.) is a low and backwardly- 
directed crest, and, as in the middle region, the anterior border of the arch is very 
Posterior tlioracic vertebra of ArsinoiiJierium zitteli : A, from front ; B, from right side. 
Lettering as in text-fig. 11. 5 nat. size. 
concave, while the posterior border overhangs to a corresponding extent. The 
anterior zygapophyses {a.z.) are now concave from side to side, and external to tliem 
there are prominent metapophyses connected by a ridge wdtli the stout, somewhat 
backwardly-directed, transverse ])rocesses. The outer ends of the transverse processes 
bear small tubercular facets {t.f.). Tlie ])ost('rior zygapojihyses {p.z.) are prominent 
and convex from side to side. Tlie capitular facets {c.f.) are nearly circular and 
are borne on short jirocesses rising from the side of tlie neural arch above the 
level of the neural surface of the centrum. 
Still further back the centrum is deeper in ])roportion to its width, and the 
transverse jirocesses are more prominent and less massive, while the neural arcli 
is still lower. 
!n the lumbar region the vertebra; become much depressed, till in the hinder 
