388 



Harriet Lehmann, 



and establishes an identity as regards the place of origin for the 

 pulmonary artery in all lung-breathing vertebrates. The diagrams 

 of Boas have accordingly replaced those of Rathke. 



Nevertheless , there are still considerable gaps in our know- 

 ledge of the aortic arches, and an illustrated account of their actual 

 condition and course of transformation is to be desired, especially 

 for mammals. 



The rowth of knowledge in reference to these arches, leading 

 up to the present time, is best exhibited by a brief review of the 

 literature, which will accordingly form the first topic for con- 

 sideration. 



Résumé of tlie literature. 



As mentioned above, the aortic arches were described and figured 

 by Malpighi in 1672. In that year he sent to the Royal Society in 



London two separate memoirs on the 

 development of the chick both of which 

 were amply illustrated. Text-Fig. A 

 is copied from a sketch in his "De 

 Formatione Pulli in Ovo", and serves to 

 show that aortic arches were distinctly 

 seen by this clear-sighted observer. 

 He gives sketches of the aortic arches 

 in different figures, but they are shown 

 for one side only, and it is fair to 

 assume that he did not understand these 

 structures as existing in pairs. 



So far as I am aware the first 

 paper treating of the aortic arches in 

 any critical manner, is that of VON Baer, 

 in 1827. In this paper he describes 

 Sketch of one of Malpighi's Figs, the aortic arches of birds in more 

 (1672), showing the heart and aortic jj^tail than in other vertebrates. He 

 arches. Letters as m the oriffmal: . , ,t , n • x- j- -u 



A vein, B auricle, D right ventricle, ^^^^^^ ^^'^^ ^^^ P^^""! ""{ ^°r^\« ^^«^^«, 

 F, G aorta. are present, at least m the embryos of 



all vertebrates which develop out of 

 water, but are never all present at one time. Of these arches, the first 

 two pairs, and the fifth of the left side, completely disappear. The third 

 arch of either side becomes the common stem for the arteries to the head 

 and fore-limb, and the fourth arch of the right side becomes the arch of 

 the aorta. The fifth arch of the right side and the fourth of the left 

 are transformed into the two pulmonary arteries. The short common 

 stem of these two arteries is formed while the truncus arteriosus is divided 

 into two channels. In mammals, he says, the changes are similar, but 



Fig. A. 



