1. A general anatomic nomenclature for a circular or ringlike structure; also written as annulus; however, some sources state that the spelling anulus is currently preferred.
2. In zoology, a ring-shaped structure; such as, any of the external segments of an annelid worm.

A thickened portion of the vascular tunic of the eye between the choroid and the iris.

It consists of three parts or zones: orbiculus ciliaris, corona ciliaris, and ciliary muscle.

The lesser ring of the iris; the more coarsely striated inner concentric circle on the anterior surface of the iris; also called "lesser circle of iris".

Either of two zones on the anterior surface of the iris, separated by a circular line concentric with the pupillary border.

A cardiac lymphatic ring which is a chain of lymph nodes (paracardial lymph nodes) around the cardiac opening of the stomach.

A muscular ring surrounding the fossa ovalis in the wall of the right atrium of the heart.