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embryos of lacerta, which was sufficient in all respects. Therefore 
| shall begin with a description of my experiences with lacerta. 
For further elucidation the shoulder girdle and sternum of an 
adult lacerta agilis have been drawn from nature in diagram 1. 
The whole complex has been drawn in a plane. One may observe 
that at both sides of the prosternum three ribs are inserted by 
syndesmoses, and that the xiphisternum supports two ribs. It would 
be better to speak of two xiphisterna here, as at the level of the 
fifth rib there is only a syndesmotie connection in the median plane. 
Prosternum and xiphisternum are also connected by syndesmoses 
Coracoideum (hatched) and sternum are connected by a diarthrosis; 
the coracoidenm fits in a groove, sulcus articularis coracoideus, of 
the sternum. Clavicula and episternum, which are further left out 
of consideration, are dotted. 
In the prosternum we find a fontanel closed by membrane. 
The youngest embryo at my disposal, Lacerta ag. D. (N:T.*) about 
22) had not yet any sternal formation. Neither was there anything 
to be found of the shoulder girdle as yet. Only in the extremity a 
thickening of the mesenchym, the first formation of the humerus, 
was found. 
The next embryo, Lacerta ag. S. (N.T. about 24) differs from the 
preceding one in so far that the formation of the shoulder girdle, 
continuous with that of the humerus, is visible. As this shoulder 
girdle is as yet very vaguely outlined, one can hardly distinguish 
any shape in it, at most a ventral coracoidal part and a dorsal 
scapular part. Now if one looks more in a caudal direction, one 
finds in the sidelong wall of the trunk a densening of the mesenchym, 
which js unconnected with any other skeleton-formation. This is the 
first formation of the sternum, which as yet consists exclusively of 
blasteme, dense mesenchym. In diagram 2 a transversal section has 
been drawn, in which there is a sternal formation. The section is 
not quite transversal; in the lower part we see the humerus, in 
the upper part radius and ulna. Still the left hand as well as the 
right hand sternal formation are present in the section. This proves 
that the sternal formation has already been extended in eranio- 
caudal direction. It is not possible to demonstrate in pictures of 
transversal sections the independences of the sternal formation of the 
humeral zone (in casu the coracoideum). As will appear later on 
the more obliquely sectioned series of Gongylus ocellatus. are better 
suited for this purpose. 
1) Normentafel. Lacerta agilis von K. Perer. 
