VIII.] 



THE DUCTUS BOTALLI. 



219 



chiefly in the complete separation of the pulmonary and 

 systemic circulations. 



Diagram of the Arterial System of the Adult Fowl. 



JR.I.N. right innominate artery. The other letters as in Fig. 66. 

 The dotted lines, as before, shew the portions of arches which have been 

 obliterated. 



As the branches to the lungs become stronger and 

 stronger, less and less blood from the right ventricle enters 

 into the dorsal aorta; and the connecting vessels become 

 smaller and smaller. 



Each of the arches from the right ventricle may therefore 

 be considered at about the sixteenth or eighteenth day as 

 divided into two parts, an inner part which connects the heart 

 with the lung, and an outer part which still connects the arch 

 with the main dorsal aorta. As these outer parts become 

 smaller they receive the name of the 'ductus or canales 

 Botalli' or 'ductus arteriosi.' The one on the right side is 

 short ; that on the left side is much longer and narrower. 



Von Baer supposed that the reason of this was, that since the pulmonary 

 arch of the left side was the fourth, the ductus Botalli of that side consisted of 

 the branch between the fourth and fifth arch, as well as between the fifth arch and 

 the dorsal aorta. It is easy however from diagram (Fig. 66) to see that this 



