438 ME. ST. GEOEGE MIVAET 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 jiostaxial end the ischium in the adult expands into a subquadrate dorso- 

 ventrally expanded plate of bone (fig. 71, i) 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. 



The Ribs. 



The ribs consist of two series, the vertebral and the sternal ribs, the former series 

 being the more developed both in number and size. 



The Vertebral Ribs. 



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 vertebrcE. 



Five of the vertebral ribs articulate with sternal ribs, which themselves join the 

 sternum directly by distinct articular surfaces (fig. 1, iv, v, vi, vii, & viii). 



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 ventrally 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 Bib. 



This little rib (fig. 75, i) is attached to the eighteenth vertebra, and very often 

 anchyloses with it. It is a flat bone, subtriangular in shape, with its three margins 

 concave, 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 cajjitulum (h), and a tubercle or tuberculum 

 (t), subsequently developed to articulate respectively ^vith 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. 



