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sternal formation is not clearly separated from that of the coracoi- 
deum; the cause of this state of things lies in the fact that the two 
have grown in each other’s direction. The humerus is here for the 
greater part built up of cartilage. The ribs are still separated from 
the paired sternal formation by loose mesenchym. 
Still further developed are Gong. ocell. C and D. They have a 
breastbone formation that is clearly separated from the coracoideum 
by a thin dividing layer, the formation of the diarthrose. The stage 
in which the division of sternum and coracoid was almost impossible, 
is over here. The three ribs, which end within a short distance of 
the sternum are still entirely unconnected with A. The sternal 
formation does not reach further caudally than the third rib. 
The embryos E and J of Gong. ocell., too represent one and the 
same stage. As a basis for description I take embryo E. Sternum 
and coracoid are definitively separated. Three ribs are connected 
with the praechondral prosternum by mesenchym that is moderately 
dense. 
A caudal blastematic offshoot of the sternal ridge grows in the 
direction of the fourth rib, but is still entirely unconnected with it. 
As some few sections were wanting I could not with certainty fix 
the relation between all prosternal ribs separately and the sternum. 
Undoubtedly the above said observations can be generally applied, 
as is proved by Gong. ocell. 1. In this embryo there is one and 
the same relation between each of the three ribs and the sternum, 
viz. that of a still less clear connection than in embryo E. The 
caudal offshoot of the sternal formation, too, is smaller here. On the 
other hand the relation towards the coracoid is the same. 
Embryo Gong. ocell. Iu. corresponds with embryo lacerta J. On 
both sides three ribs are joined to the sternal formation by com- 
pletely dense mesenchym. An offshoot grows in a caudal direction 
towards the fourth rib, as is shown in diagr. 6. In this diagram 
two consecutive sections out of this series have been partly drawn. 
The direction of sectioning was here frontal to the thorax. The sternal 
formation has here to a large extent shifted in medio-ventral direction 
In embryo K, lastly, the one furthest developed, the fourth rib, 
too, is joined blastematically to the sternum. For want of older 
embroys the development of the xiphisternum in Gongylus could 
not be followed any further. From what precedes it appears that 
the results obtained in Gongylus are a confirmation of the expe- 
riences in Lacerta. 
Finally, I had an opportunity to study two series of young embryos 
of Ptychozoon homalocephalum. 
