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autoclthonic sternal formation, or in other words: where are the 
divisions between the autochthonic breastbone and the ribs situated ? 
With regard to the first three vertebro-sternal ribs the answer is 
easy. Here the abovesaid divisions correspond with the definitive 
syndesmoses sterno-costales. With regard to the fourth and fifth ribs, 
in order to get certainty there, one has partly to take for basis 
magnitudinal relations such as are represented in diagram 7. In 
diagr. 7d the little crosses indicate the situation of the definitive 
sternocostal syndesmoses. It appears from the diagram that the place 
where the fourth rib has placed itself against the autochthonic sternal 
band (7c) is not the same as that where later on the syndesmoses 
sterno-costalis IV is found, but that the latter is situated at the place 
of the later division between prosternum and xiphisternum. One 
6 
Stern. 
Xiphi- 
Costa TZ w Sternum 
Coslae \ Costae 
¥ v 
Fig. 7. Lacerta agilis. Outlines of the development of the Sternum. 
may be reminded again of the fact that all syndesmoses in this 
region of the thoracic skeleton have been formed secundarily in 
places where first (7d) there was cartilaginous continuity. A conse- 
quence of this is also that one will never be able to tell exactly 
where in adult reptiles the autochthonic sternum ceases, where 
the ribs begin. I never saw the autochthonic sternal formation 
reach further caudally than the insertion of the fourth rib. On 
the other hand I did not see either that the fifth rib placed 
itself against the fourtb, while the latter did not yet form a carti- 
laginous continuity with the sternal band. Consequently one has 
again to take for basis the magnitudinal relations of diagr. 7 in 
order to come to the conclusion, probable for an abovesaid reason 
as well, that the fifth rib tries to come into contact with what was 
formed out of the fourth rib, and not with the autochthonic sternal 
