EMERSON: ANATOMY OF TYPHLOMOLGE. 
51 
amphicoelous vertebrae. Between the skull and the attachment of 
the pelvic girdle are fifteen vertebrae, differing but little from one 
another in shape and size. The sacral vertebra is the sixteenth and 
the ilia are attached to the ribs which it bears. In the caudal region 
are thirty-five vertebrae, differing in form from those of the trunk 
and from one another in size and slightly in form. 
The trunk vertebrae. — A typical trunk vertebra consists of a 
rounded centrum or body to which is attached dorsally the neural 
Lateral View. 
Fig. A. — Trunk vertebrae, x 6. Cent., centrum ; N. S , neural 
spine. 
arch, bearing a neural spine and two lateral rib-bearing processes. 
The centrum is in form like an hour-glass with a small concavity at 
each end, making the vertebra amphicoelous. The rim of the ante¬ 
rior concavity articulates with the rim of the posterior concavity of 
the vertebra immediately anterior to it. 
The dorsal aspect of the neural arch shows a broad plate. In the 
median line of the posterior half of this plate is a ridge, which be¬ 
comes very prominent posteriorly, the neural spine. The posterior 
border of the neural arch slightly overlaps the arch of the vertebra 
immediately posterior. It bears two postero-lateral processes, the 
postzygapophyses, the ventral surfaces of which articulate with the 
