noun
sacral vertebra
Anatomical term for the vertebrae that form the sacrum.
仙椎は通常、成人では癒合して仙骨を形成する。
The sacral vertebrae normally fuse to form the sacrum in adults.
仙骨 is the sacrum (the fused bone), while 仙椎 refers to the individual vertebrae that make it up.
From 仙 (sacrum) + 椎 (vertebra). The kanji 仙 is used here for its anatomical meaning related to the sacrum.