228 
of the ventral end of the fourth rib, separated from the latter by 
loose mesenchym. At the description of the embryo Gongylus ocell. 
L. one finds entirely similar relations made clear by two frontal 
sections (diagr. 6). 
Embryo Lacerta ag. L. (N.T. about 31) shows little progress as 
compared with embryo J. The principal point is that the two sternal 
ridges are here connected with three ribs by entirely densened 
mesenchym. The relation between the fourth rib and the sternum 
has not undergone any change. The extension of the praechondrium 
in the sternal formation has increased. The caudal offshoot is still 
entirely free from praechondrium. If one compares diagrams 2 and 
4, one sees that the sternum in diagr. 4 is still found at the same 
place as in diagr. 2 viz. in the lateral trunk-wall. Shifting towards 
the ventral median line has not yet taken place. In the older embryos 
following, this shifting becomes clearer and clearer. One might 
suppose some connection to exist between this shifting and the 
longitudinal growth of the ribs with which the sternal formation is 
now connected. It seems to me better to take the relative decreasing 
of the heart-bulge for the only canse of this. For though in Anguis 
the sternum and the only vertebro-siernal rib are soon definitively 
separated (WirpersHEmM), still the sternal halves shift towards the 
median line to grow into one whole there. 
In embryo Lacerta ag. N. (N. T. about 32) we find a beginning 
of important phenomena of development. In the first place a dense- 
ning of mesenchym has appeared here between the end of the fourth 
rib, and the still blastematical end of the sternum. Here is as yet 
no question of complete joining, as the intermediate zone has not 
yet reached the same state of density as the sternal formation. The 
ventral end of the fifth rib, the last of the future vertebro-sternal 
ones, is situated thirteen sections caudally (130 u) to the insertion 
of the fourth rib to the sternum in the straight ventral muscle. 
In the second place I have to mention here that, in spite of its 
further development in comparison with embryo L, the sternal for- 
mation does not reach caudally past the insertion of the fourth rib. 
From various circumstances it appears that embryo Lacerta ag. 
N. (N. T. ab. 33) is further developed than the preceding are. As 
regards the sternal formation, here too the fourth rib is connected 
with the blastematic caudal end of the sternum by completely den- 
sended mesenchym. The end of the fifth rib is situated only eight 
sections (80 u) caudally to the insertion of the fourth rib to the 
sternal band. Consequently the fifth rib has been lengthened, and 
has grown in the direction of the sternal formation. But, conversely, 
