AXTAL SKELETON OF THE OSTRICH. 409 
great lateral projection of the parapophysis, on to which here, as in the more preaxial 
vertebrie, the preaxial articular surface of the centrum extends itself. 
Superiorly the canal for the artery is bounded by a process of bone, which extends 
outwards from beside and beneath the prezygapophysis (being in fact a diapophysis, 
or tubercular process)', on the outer side of which is to be seen a prominence still 
representing the metapophysis (figs. 40 & 41, m). 
These parts exist in the same way in preceding vertebre; but they are most con- 
veniently noticed here on account of the large size they attain on the dorsal and ventral 
sides respectively of the great canal for the vertebral artery. 
The articular surfaces of the prezygapophyses look more inwardly, and those of the 
postzygapophyses more outwardly, than do the corresponding surfaces of the seventeenth 
yertebra; and the postzygapophyses also extend postaxially beyond the centrum to a 
greater degree (fig. 40, pz). 
The neural spine may be longer antero-posteriorly, and is wider transversely as well 
as more extended dorsad than is the neural spine of the preceding vertebra. 
Its anterior excavation is larger and has a nearly vertical postaxial wall, with two 
prominent ridges, which bound it laterally and proceed preaxially and nearly parallel 
to near the preaxial margin of the neural arch. 
The posterior excavation of the neural spine is at about its maximum of development 
in this vertebra, and is overshadowed and protected by the postaxial extent of its dorsal 
lateral margins, which diverge from the neural spine to the postzygapophyses. 
The pre- and postaxial margins of the neural arch are strongly concave, though the 
former is not so much so as is the corresponding part in the seventeenth vertebra. 
Sometimes two conspicuous foramina lead into the substance of the bone on either 
side. One of these is placed a little on the ventral side of the interzygapophysial 
ridge, rather nearer to the postaxial margin of the pedicle of the neural arch than to 
its preaxial border; the other may be sometimes found at the side of the middle of the 
centrum, directly ventrad to the first foramen. 
THe NINETEENTH VERTEBRA. 
The nineteenth vertebra is very like the eighteenth in size and general shape, 
although it has never any pleurapophysial osseous band, but always an articulated rib 
(the second rib) instead. 
This absence of course produces a striking difference in the general appearance of the 
yertebra when it is viewed preaxially. 
The centrum presents a preaxial surface which ends in an obtusely pointed process 
on each side; and both the dorsal and ventral margins of its articular surface are less 
concave than are the corresponding margins of the eighteenth vertebra (fig. 43, ae). 
‘ The diapophysis is that part to which the tubercle of the rib is attached, while its head joins the 
parapophysis. 
Vou. vit.—PArRT vu. March, 1874. 3M 
