17 8 ELEMENTS OF ORNITHOLOGY, 
they are called Carinate birds. A keel is wanting, or more 
or less rudimentary only, in the Ostrich, Rhea, Emeu, Casso- 
wary, and Apteryx, in a single kind of Parrot, a peculiar Rail- 
like bird (Notornis), and in the singular Opisthocomus *, amongst 
existing birds. 
The lateral part of the sternum which receives the ribs, 
generally extends forwards on either side intoa more or less 
marked prolongation called the costal process. From the middle 

Sipe View or Tuorax or Fowt. 
i, Keel of sternum; m, middle xiphoid process; 7, internal lateral xiphoid 
process; ¢, external lateral xiphoid process; 7, rostrum or manubrium ; 
c, costal process; 2, hypapophysis from middle of vertebral centrum ; 
a, appendage from ribs, or uncinate process. 
of the anterior margin of the sternum—which is almost always 
convex—a single process called the rostrum or manubrium may 
project forwards and may bifureate. 
On either side, between this and one of the costal processes, 
is the coracoid groove. Sometimes (as in the Hoopoe) the 
median anterior part of the sternum is perforated to receive 
processes from the bases of the coracoids. Very rarely, ¢. g. in 
* See ante, p. 94. 
