AXIAL SKELETON OF THE PELECANIDA. 327 
postaxial end of the centrum than in the seventeenth vertebra. There are similar 
par- and diapophysial surfaces, but further apart. 
Defects of ossification, which began to appear in the preceding vertebra between 
these surfaces, on the outsides of the transverse processes, are here very conspicuous ; and 
sometimes a large oval foramen (placed between the postzygapophysis and the adjacent 
postaxial margin of the transverse process) leads into the substance of the hemal arch 
on each side. 
The NINETEENTH VERTEBRA is the first vertebra which forms, in the adult, part of the 
sacral mass, being more or less ankylosed to the vertebra next succeeding. It is 
slightly smaller, in all dimensions, than is the eighteenth vertebra; but the lateral 
defect of ossification is much larger and is the conspicuous lateral opening, the post- 
axial intervertebral foramen being much smaller than that between the eighteenth and 
nineteenth vertebre. 
The TWENTIETH and TWENTY-I'IRST VERTEBRA repeat the characters of the nineteenth, 
except that they are slightly smaller and more and more involved in the preaxiad 
extension of the iliac ossification, which completely covers the dorsum of the twenty- 
first vertebra, except that a foramen opens (dorsally to the transverse process), ex- 
tending obliquely preaxiad and dorsad. 
The rib-surfaces are rather less far apart in the twenty-first than in the twentieth 
vertebra ; in the latter they are at their maximum of separation. 
The TWENTY-SECOND VERTEBRA is still smaller, and is overlapped by the ilium itself. 
The di- and parapophysial surfaces are much more approximated. The defects of 
ossification are less extensive, though there is much individual variation in this respect. 
The dorsal end of the transverse process sends out postaxially an arched ossification 
(concave ventrally) which meets a similar but preaxially extending arched process from 
the preaxial end of the dorsal part of the transverse process of the twenty-third vertebra. 
Thus, when these vertebra are viewed laterally, there is the appearance of a bony arch 
extending up dorsally between and connecting them (Plate LIX. figs. 1 & 3, xx1). 
Tue Lumpar VERTEBRA. 
In comparing these vertebre with the so-called lumbar vertebrae of Struthio, and 
with the corresponding vertebra of most of the other Struthionide, a striking difference 
is apparent. It consists in the marked differentiation which exists in Pelecanus between 
those more preaxial lumbar vertebre which send out parapophysial transverse pro- 
cesses, and those more postaxial ones which only develop ascending diapophysial 
processes, and thus leave a wide interval between their vertebral centre and the aceta- 
bula—i. ¢. a lateral acetabular or renal fossa on each side, as will be more fully noticed 
in describing the ventral aspect of the pelvis. 
These vertebre, therefore, are more evidently divisible into true /umbar vertebra and 
