The morphology of the basilar artery and its branches was studied in 52 human brains with special reference to arterial anastomosis, and its course and distribution on the pontine ventral surface. The results were as follows:
1. Main trunk of the basilar artery
(1) The average maximum and minimum external diameter was 3.93 ± 0.76 mm and 3.14 ± 0.58 mm, and the average length was 35.0 ± 5.1 mm.
(2) Fenestration was observed in one case (1.9%).
(3) The shape of flexion was classified into three types: S-shaped (18 cases=34.6%), inverted S-shaped (29 cases=55.8%) and straight (5 cases=9.6%).
(4) The average angle of flexion was 32.5 ± 24.5°. A positive correlation was observed between age and the angle of flexion; the coefficient was 0.31.
2. Branches of the basilar artery
(1) The average number of branches from the main trunk of the basilar artery was 22.8 ± 3.94. The main trunk was divided into three equal portions: the rostral, intermediate and caudal. Of all the branches, 43.9% arose from the rostral portion, 33.3% from the intermediate portion and the remaining 22.8% from the caudal portion.
(2) Forty-eight percent of all the branches had an external diameter ranging from 0.35 mm to 0.55 mm, and this size was predominant in the branches from each of the three portions.
(3) Of all the branches, 45.4% had a diverging angle between 45°and 90°. This was the predominant range of diverging angle in the intermediate and rostral portions. In the caudal portion, however, the predominant diverging angle tended to range from 0° to 45°.
3. Arterial anastomosis, course and distribution on the pontine ventral surface
(1) Ninety-nine anastomoses were found on the pontine ventral suface in 42 cases. Fifty-seven anastomoses (57.5%) were found between pontine branches and 21 (21.3%) between a pontine branch and an anterior inferior cerebellar artery. More anastomoses were
Correspondence to Yoh Nishijima, Department of Anatomy, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113, Japan found in the median area than in the lateral area.
(2) A number of arterial distributions were observed along the basilar sulcus in the middle and lower parts, around the facial and vestibulocochlear radices and around the trigeminal radix. Many branches had a downward distribution along the basilar sulcus in the middle and lower parts, an outward distribution around the facial and vestibulocochlear radices, and a downward or outward distribution around the trigeminal radix.
(3) Of all the trigeminal radices, 55.8% were supplied only with pontine branches, 1.9% only with an anterior inferior cerebellar artery, and 36.5% with both of them.