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Philippine Journal of Science 
1919 
formation was done by von Baer(i) in 1827. The last-named 
author claimed that five pairs of aortic arches were present in the 
embryos of all vertebrates that developed out of water, but that 
these were never all present at any one time. Thirty years later 
Rathke (7) drew up schemes to represent their transformation in 
Amniota, based upon the assumption that there were only five 
pairs of these arches represented in the embryonic stage of the 
higher vertebrates. For a long time the diagrams of Rathke 
were accepted as standards to represent the history of the de- 
velopment of these arches. 
Lehmann (5) says: 
The number of arches recognized by Rathke however was thrown into 
question by van Bemmelen in 1886, who first pointed out the presence 
in reptiles and the chick, of a rudimentary arch between the fourth and 
the supposed fifth. Subsequent observations, notably those of Zimmermann 
(1889), and Tandler (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 the aortic arches for Amniota the same 
as in Dipnoi and Amphibia, and establishes an identity, as regards the 
place of origin of the pulmonary artery in all lung-breathing vertebrates. 
The diagrams of Boas have accordingly replaced those of Rathke. 
Evans, (3) writing in Keibel and Mali’s Human Embryology 
on abnormal aortic branchings, says in part: 
The variations in the great vessels arising from the aortic arch have been 
known for a long time and could be explained satisfactorily on an embryo- 
logical basis ever since the work of Rathke. (1843). 
To explain my cases of abnormality of origin, it would seem 
advisable to review the development and transformation of the 
aortic arches and segmental arteries occurring in normal mam- 
malian embryos (see figs. 1 and 2). In human embryos 4 to 5 
millimeters in length five aortic arches are recognized to develop 
in the following order: First, second, third, fourth, and sixth. 
The fifth aortic arch is transitory, appearing in embryos 7 mil- 
limeters long; it soon degenerates. 
Both the descending or dorsal aortse, between the first and 
third arches, together with the third aortic arches, give origin 
to the internal carotid arteries; while the two ventral aortse, 
between the third and fourth arches, form the common carotids ; 
those between the first and third arches become the external 
carotids after the disappearance of the first and second aortic 
arches. The portion of the dorsal aorta between the third and 
fourth arches disappears. 
The fourth arch, including the short ventral stem between 
the fourth and sixth arches, becomes the permanent aortic arch 
