The arterial arches and their interpretation in Bipes and other amphisbaenians

The study of the arterial arches of Bipes, the only amphisbaenian with forelimbs, resolves the problem of the interpretation of the structure of the arterial arches in other forms of this group of squamate reptiles. In Bipes, as in turtles, the subclavian and common carotid arteries originate from a brachiocephalic trunk, which arises from an innominate trunk deriving from the right aortic loop. This interpretation is not only original but also emphasizes the important lengthening of the brachiocephalic part relative to the strictly carotidian one. It supposes the intercalation of a new "precardiac" region between the pectoral girdle and the heart; these two components are closely associated topographically in the quadrupedal Squamata. This lengthening, expressed by the increase in the number of precloacal vertebrae, is linked with the increase in the asymmetry of the aortic loop.