289 
he concludes that there are in human and rabbit embryos six pairs of 
aortic arches and five entodermal branchial pouches. Although 
ZIMMERMANN exhibited his specimens before the German Anatomists his 
published descriptions are not accompanied by illustrations. 
The very desirable feature of supplying illustrations of the aortic 
arches in mammals was met by TAnpLEer who, in 1902, published 
figures and descriptions of the conditions as he found them in rat and 
human embryos. In the rat he found no complete fifth arch but ir- 
regular rudiments which were supposed to represent it. In the human 
embryo, however, he represents reconstructions of two cases (see Figs. 9 
and 10) which show a fifth arch, but, in neither case do the anatomical 
relations exactly correspond with those in the embryo investigated by 
ZIMMERMANN. 
Up to this time there had been little dissent to regarding all 
these findings as evidence of the existence of six arches in mammals, 
but, in Dec. 1903, F. T. Lewis, in a preliminary paper before the 
Association of American Anatomists, called attention to the very ir- 
regular condition in the rabbit of the vascular elements between the 
systemic and pulmonic arches and expressed the conclusion that „The 
irregular small arteries around the fourth entodermal pouch do not as 
ZIMMERMANN believed, form a distinct aortic arch”. 
Harriet Lenmann, in 1905, published descriptions and illustrations 
of the condition of the aortic arches in pig and rabbit embryos. Her 
observations agree in essential features with those of Tanpier on the 
rat and human embryos. In the rabbit!) her specimens showed ir- 
regular and disconnected arteries between the systemic and pulmonic 
arches but in no case was a complete arch observed. In the pig 
embryos studied by Miss Lreumann the condition of these vessels was 
less irregular and showed a complete vessel passing from the fourth 
to the pulmonic arch and connected by an independent branch with the 
aortic root (see Fig. 10). 
In Dec. 1905, there was presented before the Association of Ame- 
rican Anatomists a further account of the observations of Dr. F. T. 
Lewis?) on the aortic arches of both rabbit and pig embryos showing 
great irregularity of the small arteries between the sytemic and pul- 
monic arches and lack of correspondence between these vessels on the 
two sides of the embryo. 
It was maintained on the basis of these observations that the evi- 
dence of the existence of six aortic arches in mammals is ambiguous 
1) The rabbit material was obtained, primarily fcr another re- 
search, from the Harvard Collection through the courtesy of Dr. Minor, 
but was used to supplement Miss Leumann’s already completed observ- 
ations on the aortic arches of the pig, without knowing at the time, 
that the same ground was being covered by Dr. Lewis in the Harvard 
Laboratory. Observations on the aortic arches of vertebrates having 
been carried on since 1899 in the laboratory in which she was working. 
2) In the absence of Dr. Lewis the paper was read and discussed 
by Dr. Miwor. 
Anat, Anz, XX]X. Aufsätze, 19 
