Spina vestibuli, or vestibular spine, is a bony structure, in anatomical terms a 'mesenchymal condensation', which extends from the mediastinum of the heart and covers the leading edge of the primary atrial septum; its origin is outside of the heart. Below the opening of the orifice of the coronary sinus they fuse to form a triangular thickening — the spina vestibuli.
The spina vestibuli is an anatomical formation that arises from outside the heart and extends into the mediastinum, covering the primary atrial septum. It later merges with another structure to create a distinctive triangular thickening.