Calcarine spur

The calcarine spur (a.k.a. calcar avis) is a longitudinal prominence on the medial wall of the atrium and occipital horn of the lateral ventricle. It is produced by the inward indentation of the calcarine sulcus (calcarine fissure).

Relationship to the bulb

The calcarine spur lies inferior to the bulb of the occipital horn (bulb of the corpus callosum). Together, the calcar avis and bulb form the characteristic contour of the medial wall of the atrium and occipital horn.

Key concept

• Calcarine sulcus → inward indentation → calcar avis,

• Whereas forceps major → bulb of the occipital horn.