AVIAN INTERCAROTID ANASTOMOSIS AND ITS HOMOLOGUE IN OTHER VERTEBRATES

Intrasphenoid and intrasellar segments of the cerebral carotid arteries were dissected in 82 specimens of birds, representing 21 avian orders. The configuration and branching of these carotid segments and the intercarotid anastomosis were observed. A well develop intercarotid anastomosis unites the two carotids directly caudal to the hypophysis in all birds examined except for five specimens of passeriform birds of the Suborder Tyranni. Three principal patterns occur: an H‐type having a lengthy transverse anastomosis connecting the carotids; an X‐type with the carotids anastomosing side‐to‐side; and an I‐type with the carotids merged into a single longitudinal vessel. Patterns for each species are illustrated. Since ordinarily birds lack a cerebral arterial circle comparable to that of mammals. the intercarotid anastomosis obviously serves as its substitute. Evidence of correlation between asymmetry of caudal rami of the cerebral carotids and form of the intercarotid anastomosis is presented. A communication between cerebral carotids caudal to the hypophysis seems to be a deep‐rooted vertebrate characteristic. An intercarotid anastomosis, apparently homologous to that of birds, occurs in a number of cartilaginous fishes, reptiles, and mammals. In mammals the intercarotid anastomosis is a communication between right and left posterior hypophyseal arteries. Copyright © 1968 Wiley‐Liss, Inc.