Morphological variations in the transverse foramen of the axis in Japanese serows (Capricornis crispus).

The presence of transverse foramina in the axes of Japanese serows, a special national natural treasure in Japan, has been reported to be unstable, but other variations are unknown. In this study, we analysed the shape, cross-sectional area, length, and volume of the transverse foramen in the axes of 19 specimens using gross anatomy and computed tomography (CT) scan. There were four types in the transverse foramen: type 1, having the transverse foramina; type 2, having two cranial openings; type 3, sifting a caudal opening to the ventral side of the transverse process; and type 4, having no transverse foramina. Although the transverse foramina showed different types on the left and right sides in several specimens, there were no statistically significant differences in the length and volume. This variation may be related to running patterns of the vertebral artery penetrating the transverse foramina. Two goats without the transverse foramina were examined to infer a running pattern of the vertebral artery instead of Japanese serows. The vertebral artery in the goats branched in two directions (spinal and muscle), between the axis and the third cervical vertebra. This passage of the goat vertebral artery might be presumed in type 4 of Japanese serows. This study reveals the instability of the transverse foramina in the axes of Japanese serows and provides new data to compare the axes of other ruminants.