On the vascular architecture of the carotid labyrinth in Cynops pyrrhogaster and Onychoactylus japonicus.

The fine vascular arrangement of the carotid labyrinth in two species of urodeles, Cynops pyrrhogaster and Onychodactylus japonicus was investigated. India ink-gelatin injected preparations were examined under the dissecting microscope. Resin casts of the blood vessels prepared using the method of MURAKAMI (1971) were observed in the scanning electron microscope. In both species, the common carotid artery terminated in the central chamber from which arose two retia mirabilia, i.e. an external carotid rete and an internal carotid rete. The external carotid artery arose recurrently from the external carotid rete, whereas the internal carotid artery received vessels from the internal carotid rete which apparently occupied more than two thirds of the carotid labyrinth. The present observations indicate that the previous descriptions of the urodele carotid labyrinth should be corrected: a vascular ring exists around the common carotid artery and the latter shows a corresponding narrowing at the entrance to the carotid labyrinth; the vascular ring forms the most proximal part of the external carotid rete; the central chamber occupies only a part of the proximal end of the carotid labyrinth; the internal carotid rete and the external carotid rete constitute a continuous rete mirabile; and a distinct furrow exists in the boundary between these two portions of the rete mirabile. Individual variations were frequently encountered, but were confined to the external carotid artery and its tributaries. The complicated and elaborate vascular architecture of the amphibian carotid labyrinth suggests that this organ should exert blood-flow regulating the probably other unknown functions as an effector organ in addition to its accepted activity as a chemo- and baro-receptor.