STERNUM 909 
cartilage on either side. Thereupon the lateral portion of the first 
2 or 3 Ribs is absorbed, so that the anterior portion of each band 
loses its connexion with the vertebral column, and is transformed 
into a ribless process, the future processus lateralis anterior of the 
Sternum, the dorsal part of these reduced Ribs remaining as cervico- 
dorsal Ribs (p. 788). A similar reduction or withdrawal of 2 
or 3 Ribs takes place at the posterior end of each band, trans- 
forming it into the processus lateralis posterior. In the mean- 
while both bands have met in the middle line, and fuse together, 
from the anterior end backward, thus forming the sternal plate or 
body of the Breastbone. The inner margins of the bands, how- 
ever, do not unite smoothly, but turn downward, producing two 
ZEAL: 
Earty AND LATER STAGES OF THE DEVELOPMENT OF THE CHICK’s STERNUM. 
C.B. sternal bands ; Mt. Metasternum ; P.l.a. P.l.p. and P.obl. Processus lateralis anterior 
posterior and obliquus; R. Rostrum; 2.1-10, Ribs. 
median ridges which are the foundation of the future Keel (cf, 
CARINATA, p. 76). The sternal plate now develops considerably 
posteriorly, forming the Mefasternum, which, not being directly caused 
by withdrawing Ribs, is not homologous to the Xiphosternum of other 
Vertebrates, whose equivalent is the two posterior lateral processes. 
This Metasternum grows to a great length in many Birds, so that, 
as in the Gallinx, it may form the most conspicuous part of the 
whole, and the same remark applies to the posterior lateral processes 
from the lateral margin of which grows out in many Birds a processus 
obliquus. The anterior end of the Sternum receives in facets the 
distal end of the Coracoids, between which grows out a median 
apophysis, the rostrum or spina sternalis, which serves chiefly for the 
attachment of the ligaments which connect it with the CLAVICLEs, 
and also close the whole space between them and the Coracoids, 
