側頭骨内における顔面神経の形態について

抄録

The material consists of 12 Japanese, 6 male and 6 female, skulls, which were obtained from the Department of Anatomy, Nippon Medical School. After exposure of the facial nerve in the bone using the drill, the specimens were projected on three planes : horizontal O-A-E, sagittal P-S-E and frontal P-F-E. On these projections the course and the lntgth of the facial nerve were investigated.
1. The first labyrinthine portion, from introitus to genu, was mostly convexed lateralward, and was straight in the other cases. The site of the genu was anterior to, and mostly lateral and superior to the introitus.
2. The angle at the genu can be divided into medial and lateral angles through sagittal line on horizontal plane. The medial angle was smaller than the lateral one.
3. The second tympanic portion was seldom straight, more often slightly convexed up-, lateral- or up-lateralward.
4. When the first portion was situated sagittal or a little medial at the genu (4 examples), the second portion was convexed lateral- or up-lateralward, when the first a little down-lateral at the genu (5 examples), the second was convexed up- or up-lateralward.
5. The third mastoidal portion began at the height of the pyramidal eminence (17 ex.), seldom higher (1.5 mm) or lower (1.6 mm).
6. The height of pyramidal eminence may be the transition point from the second to the third portion.
7. The third portion was either straight or slightly curved.
8. In one example among 24 the branching of the chorda tympani was not in the bone, but distal to the stylomastoid opening.
9. The total length of the facial nerve was 30.37 mm in the mean, being the first portion 13.3 %, the second 40.0% and the third 46.7% of the total length. There was no sex, nor side difference.
10. Four points of the facial nerve including introitus, genu, height of pyramidal eminence and stylomastoid opening were more stable toward the point pyramidal eminence than toward the point porion.