438 MR. ST. GEORGE MIVART ON THE 
a ventrally extending prominence (figs. 71 & 73, ps), which approaches the pubis very 
closely, and nearly divides a small oval preaxial part of the obturator foramen from a 
very elongated and large postaxial portion. 
The shaft of the ischium is divided by three longitudinal ridges:—one well marked 
and dorsal in position; another ventral, and only marked at the more postaxial part of 
the shaft ; a third external and very marked, extending from the process approaching 
the pubis to the postaxial extremity of the bone. 
At its postaxial end the ischium in the adult expands into a subquadrate dorso- 
ventrally expanded plate of bone (fig. 71,7) more or less convex externally for the 
greater part of its extent. 
The ischium extends postaxially beyond the ilium, relatively more in the young 
condition than in the adult bird. 
Tue Riss. 
The ribs consist of two series, the vertebral and the sternal ribs, the former series 
being the more developed both in number and size. 
Tue VERTEBRAL Riss, 
Of these there may be said to be normally ten on each side, though the first and last 
of these very generally appear in the form of anchylosed transverse processes of their 
respective vertebre. 
Five of the vertebral ribs articulate with sternal ribs, which themselves join the 
sternum directly by distinct articular surfaces (fig. 1, 1v, v, v1, vu, & vit1). 
Behind these there are normally two ribs, which end freely at their ventral extremities ; 
but there may be three such ribs. In the latter case the first of these may be continued 
on yentrally by a distinct, curved, rod-like bone, which bone does not reach the sternum, 
but is applied to the ventral side of the sternal rib next in advance. 
The First Rib. 
This little rib (fig. 75,1) is attached to the eighteenth vertebra, and very often 
anchyloses with it. It is a flat bone, subtriangular in shape, with its three margins 
concaye, but especially the preaxial margin. Its length only exceeds its breadth by one 
quarter, if so much, of the latter, and is less than half that of the centrum of the 
vertebra to which it is attached. It projects freely postaxially at its distal end; and 
preaxially it presents a head and neck, or capitulum (h), and a tubercle or tuberculum 
(¢), subsequently developed to articulate respectively with the para- and diapophysis. 
Both capitulum and tuberculum are broad and rather flattened pre- and postaxially, 
being less slender and less rounded than the distal end of the rib. 
The capitulum exhibits scarcely any distinct rounded articular surface; but the 
tuberculum shows a flattened, slightly excavated facet at its extremity. 
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