[TA] one of two dilated parts of the internal jugular vein, especially evident via contrast radiography (venography): (1) the superior bulb (Heister diverticulum) is a dilation at the beginning of the internal jugular vein in the jugular fossa of the temporal bone (bulbus superior venae jugularis [TA]); (2) the inferior bulb is a dilated portion of the vein just before it reaches the brachiocephalic vein (bulbus inferior venae jugularis [TA]). SYN: jugular bulb. SYN: bulbus venae jugularis [TA].