Vertebrates usually show evidence of six aortic arches in development, suggesting that this was the primitive condition. (The greater number in the living jawless vertebrates, lampreys and hagfishes, may represent a later addition of more posterior arches.) No extant vertebrate retains 6 aortic arches (arch 1 is always absent), but this first arch can be seen in the embryology of vertebrates.
© 2007-2010 Christine Janis, Professor of Ecology and Evolutionary Biology
Colleen Brogan '10, Student Technology Assistant
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