annulus, anulus

Pl. annuli, anuli [L.] a small ring or encircling structure.

• atrioventricular a. — a ring of Purkinje cells around the right A-V orifice that serves the myocardium and valves locally and also serves as an alternative connection between the atria and the ventricles.
• fibrocartilaginous a. — the circular pad which connects the tympanic membrane to the external acoustic meatus.
• annuli fibrosi — 1. four fibrous rings at the base of the heart to which the myocardium is attached, one around each A-V orifice and one each around the aorta and the pulmonary artery.
— 2. the intervertebral disks consist of a soft central pulpy nucleus and a peripheral annulus fibrosus.
• a. iridis — the iris consists of two rings, an inner smooth annulus iridus minoris, and an outer plicated part, the annulus iridis major.
• a. preputialis — the ring of skin marking the entrance to the cavity of the prepuce.
• a. sclerae — a roll of connective tissue on the inside of the sclera at the corneoscleral junction.
• spermatic a. — a small ring condenses around the proximal centriole of the spermatid.
• a. vaginalis — the ring through which the peritoneal cavity connects with the cavity of the vaginal tunic.