56 The Alligator and Its Allies 
two articular surfaces, an anterior and more medial 
one for articulation with the head of the rib (3) and 
a posterior and more distal one for articulation with 
the tubercle of the rib. These two surfaces ap- 
proach each other as the vertebre are followed 
caudad until, in the last two thoracic vertebre, 
they form practically one surface. The processes 
of the pre- and postzygapophyses spring from the 
arch at the base of the transverse process; the 
former surface is directed dorsally and medially, 
the latter ventrally and laterally. The interverte- 
bral foramina are smaller and more nearly circular 
than in the cervical region, and are more closely 
surrounded by bone. 
The Lumbar Vertebre. The five lumbar vertebre 
are essentially like the thoracic except that the 
transverse processes, which, of course, bear no ribs, 
are both shorter and narrower. ‘The postero- 
lateral border of the centrum of the last of these 
five vertebre has a small surface for articulation 
with the antero-medial border of the transverse 
process of the first sacral vertebra. 
The Sacral Vertebre (Fig. 18, B). These are 
two in number. The centrum of the first is con- 
cave in front and flat behind, instead of being 
convex behind, and the second is flat (instead of 
concave) in front, and convex behind. The neural 
spine and zygapophyses are as in the lumbar region. 
Projecting laterally from each sacral vertebra, 
forming a close, sutural joint with both centrum 
