Nachdruck verholen. 

 Ubcraetzungsrccht vorbehalten. 



On the embryonic history of the aortic arches in 



mammals. 'J 



By 



Harriet Lehmaim. 



With plates 22—25 and 8 figures in the text. 



The transitory aortic arches of vertebrates as exhibiting a phase 

 of phylogenetic history, are of unusual interest. They were sketched 

 in the chick as long- ago as 1672, by Malpighi, and, in 1857, Eathke 

 drew up schemes to represent their transformation in amniota based 

 upon the assumption that there are five pairs of aortic arches re- 

 presented in embryonic stages of the higher vertebrates. His dia- 

 grams were for a long time accepted as the standard ones to 

 illustrate the history of these arches. 



The number of arches recognized by Eathke was thrown into 

 question in 1886 by Van Bemmelen, who first pointed out the pre- 

 sence, in reptiles and the chick, of a rudimentary arch between the 

 fourth and the supposed fifth. Subsequent observations, notably 

 those of Zimmermann (1889), and Tandlee (1902), have led to the 

 recognition of six aortic arches in mammals. The discovery of a 

 rudimentary fifth arch in mammals makes the number of aortic 

 arches for the Amniota, the same as in the Dipnoi and Amphibia, 



1) Contribution from the Zoological Laboratory of Northwestern 



University, Evanston, 111., U. S. A., under the direction of William 

 A. LoCY. 



Zool. Jahrb. XXIL Abt. f. Anat. 26 



