MICROANATOMY OF THE POSTERIOR PORTION OF CIRCLE OF WILLIS / 解剖学报

ABSTRACT

The posterior portion of the circle of Willis was examined in 125 adult and child brains under 6～40 magnification. The following results were obtainedThe terminal segments of the two internal carotid arteries were mostly equal in size (47.20?4.46%). An average of 2.5 perforating branches commonly arose from this segment distal to the origin of the posterior communicating artery. They penetrated into the anterior perforating substance, optic tract, tuber cinerum and the medial surface of the temporal lobe.The anterior choroid artery was found to originate from the internal carotid artery in 99.20?0.56% of 250 hemispheres. It usually originated laterally to the optic tract, crossed it twice, and then entered into the choroid fissure. Along its course, it sent off branches penetrating into the anterior perforating substance, temporal lobe, optic tract, hypothalamus-tractus furrow, lateral geniculate body and the uncus.The configuration of the posterior communication artery could be grouped into 4 types straight, curved, looped and plexiform of the posterior portion. The curved type was more common in adults. The PCOA gave rise to an average of 8.1 perforating branches which emerged into tuber cinerum, optic tract, hypothalamustractus opticus furrow, mammillary body, crus cerebri, and the region located between optic tract and crus cerebri laterally, and mammillary body medially. According to the variety of calibres of the PCOA, the Willis' circle could be classified into modern, primitive, transitional and mixed type.The calibre of proximal portion of the posterior cerebral artery was equal in size bilaterally in 57.60?4.4%. There was an average of 3.1 posterior perforating arteries arising from P_1. They entered into the mammillary body, interpeduncular fossa, posterior perforating substance and crus cerebri.The collicular artery and the blood supply of mammillary body were observed and briefly discussed.