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formation. So, summa summarum, the sternum of the sauria consists 
of an autochthonie (paired) prosternum and the costal, also paired, 
xiphisternum, which often continues to be two xiphisterna. Of the 
two the autochthonic prosternum is formed first. The xiphisternum 
is not formed until the paired formation of the prosternum has 
become partially unpaired (by cranial fusion). The whole process 
of development of the sternum is rendered in diagr. 7; in each part 
of this figure the sternal formation of only one half of the body 
was drawn, in diagr. 7d half of the sternum, which is already 
unpaired cranially. 
Now we have to consider what comparative anatomical conclu- 
sions we are brought to by the foregoing embryological facts. 
According to the well known manuals on comparative anatomy by 
GEGENBAUR, WriepersHem and Bürscuri the sternum of the tetrapode 
vertebrates occurs in two entirely different forms, viz. in Amphibia 
we find a sternum to the formation of which the very short verte- 
bral ribs have certainly not coöperated, and in Amniota there is 
only a costal sternum, formed by the fusion of two so-called sternal 
bands, which in their turn were formed by the fusion of the ventral 
ends of the (vertebro-sternal) ribs. Howns*') designated the sternum 
of the amphibians as archisternum and the sternum of the amniota 
he called neosternum. So in amniota the archisternum has disap- 
peared without leaving any trace and been replaced by the neosternum. 
(In passing I remind the reader of the episternal elements that may 
have been fused with the latter). So it is a generally acknowledged 
fact that the amphibious sternum has another genesis than that of 
the amniota. 
Between the sternum of the amphibians and the shoulder girdle 
there are various relations. In Urodela and the Anura arcifera the 
sternum on both sides absorbs the coracoid by diarthrosis in a sulcus 
articularis coracoideus, just as in the Sauria. In the Anura firmi- 
sternia on the contrary the two coracoids are joined to the sternum 
by synarthrosis. The two epicoracoidea, too, are here fixed to each 
other, so that the sternum here behaves like a caudal appendix to 
one solid complex, which consists of the shoulder girdles on each 
side. Researches into the development of the sternum of the amphi- 
bians have been made by Görre and WinpersHEim. According to 
Görrr®) the first formation of the sternum is originally paired. After- 
wards it fuses into one whole with the point of the arch of the 
abdominal ribs. 
1) Howes. „Nature”. Vol. 43. NO. 1108, p. 269. 
2) Görrr, Entwickl.gesch. der Unke. Leipzig 1875. 
