Anatomy. — “On the development of the slernum in reptiles”. By 
Car. VAN GELDEREN. (Communicated by Prof. L. Bork). 
(Communicated at the meeting of June 25, 1921). 
Comparative anatomy generally indicates as sterna those parts of 
the skeleton that lie in the ventral median line of the trunk-wall. 
In the reptiles, which will be discussed in this paper, we have to 
distinguish between episternum and sternum s. strictiori. The sauria 
and crocodilia possess a sternum s. str.; with the exception of the 
rhiptoglossa they bave an episternum besides. Considering the uncer- 
tainty existing about the development of the above named sterna, 
for the present only the histological build of the adult reptiles may 
be named as the only difference between the two. The episternum 
consists of bone, the sternum s. str. of cartilage, which is often 
calcified. This communication only concerns itself with the devel- 
opment of the sternum s. str. 
We owe to Raruxr the first data about the development of the 
sternum, in reptiles as well as in birds and mammals '). He found 
in Lacerta agilis, that in early embryonic stages the sternum con- 
sisted of two entirely separated parts. Each part was a strand of 
tissue consisting of a dense mass of cells, which connected the 
ventral ends of the future vertebro-sternal ribs. Afterwards the two 
sternal parts fused in cranio-caudal direction. In Anguis fragilis, on 
the contrary Ratake found that the sternum developed apart from 
the ribs. Later ?)on Ratuxe published his experiences in embryos of 
crocodiles. They were entirely in accordance with those in Lacerta. 
One cannot conclude from Ratuke’s works whether he saw any 
fundamental difference between the two ways of development of 
the sternum described above, separated from the ribs in anguis 
connected with the ribs in lacerta and erocodilus; neither can one 
conclude whether in his opinion there is a genetic relation between 
the sternum and the ribs in lacerta and crocodilus, in other words, 
whether the sternum is a product of the ribs inserted into it. 
1) H. RatuKe. Ueber den Bau und die Entwickl. des Brustbeines der Saurier 
Königsberg 1858. 
2) H.RatHKe. Ueber den Körperbau und d. Entwickl. der Krokodile. Braunsch- 
weig 1866. 
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Proceedings Royal Acad. Amsterdam. Vol. XXIV 
