Annulus

(an'-u-lus). A ring-shaped or circular opening. A circular or rounded margin. In biology, an encircling band, as those about the capsules of mo es; the spore-cases of ferns, the mantle. Cf. Molluscs, etc. A. abdominal is, the external and internal abdominal rings. A. abdominis, the inguinal ring. A. ciliaris, the boundary between the iris and choroid. A. fibros us, the external part of the intervertebral discs. A. membrani tympani, an incomplete bony ring that forms the fetal auditory proce of the temporal bone. A. o eus, the tympanic plate. A. oval is, the rounded or oval margin of the Foramen ovale. A. sub genital is, a firm, cartilaginous-like, sub genital ring, the supporting plate of the subumbrella in medusae. A. tracheae, any tracheal ring. A. umbilicus, the umbilical ring. A. of Vieu ens. Same as A. oz'alis.