223 
two autochthonie sternal bands, and moreover out of a third, also 
autochthonic, median formation. This median formation is independent 
of the sternal bands, and also of the shoulder girdle. This appears 
most clearly by the fact that the median formation is present also 
there where the clavicula is absent, so where the shoulder girdle 
does not reach the sternum. Hanson’) sees in the median formation 
part of a large blastema with the shape of a horse-shoe, out of which 
the two shoulder girdles and the cranial part of the sternum are 
formed. 
All biologists who examined the development of the reptilian 
sternum agree that the sternal bands are fused after their becoming 
cartilaginous. And after that, calcification may follow. 
In order to get an opinion founded on personal observation I 
examined a number of sauria-embryos. My experiences may follow 
here. 
For this examination I had at my disposal a dozen embryos of 
Gongylus ocellatus, sectioned into series, and two of Ptychozoon 
homalocephalum. Besides, transversal series were made of some 
Clavicula. 
7 
io 
| fh Humerus. 
x 
~ 
ee ad 
(} ~~ Prosternum. 
I 
ss : Ir 
Ir 
Bet Co stae. 
TRD SAA 
ip ee “SX iphi sternum. 
Fig. 1. Sternum and shoulder girdle of Lacerta agilis. 
sixteen embryos of Lacerta agilis. All series had been sectioned 10 u 
thick, most of them had been coloured with haematin. The develop- 
ment of the sternum could be very well observed in this series of 
1) F. B. Hanson. Americ. Journ. of Anatomy. Vol. 26, 1919. 
tat 
