227 
diagram is to demonstrate the relation between the first rib and the 
sternal formation. In this embryo, which has reached a rather 
advanced stage of development, as is proved by the advanced histo- 
logical differentiation, still all connection between sternum and ribs 
Fig. 4. Lacerta ag. H. transversal. 
is wanting. The second and third ribs namely behave exactly in the 
same way as the first. 
The next embryo, Lacerta ag. J. (N.T. about 31) is distinguished 
from all those described above by the possession of a sternal for- 
mation, which extends in a caudal direction past the third rib. The 
sternal formation here consists of one larger cranial part, in which 
praechondrium is found and with which three thoracic ribs are 
connected by moderately dense mesenchym, and a small caudal 
part, which has the appearance of an offshoot of the former. This 
offshoot is still purely dense mesenchym and ends at a short distance 
