(ōs)
(ōr′ă)
pl. ora [L. os, stem or-, mouth]
A mouth, an opening.

incompetent cervical os

A uterine cervix that cannot maintain a diameter small enough to support the increasing weight of the fetus. This condition usually results in early second trimester abortion. The cause is a congenital structural defect or previous trauma to the cervix. It is treated with a purse-string ligature that encircles, encloses, and reinforces the cervix.

pinhole os

A very small opening to the uterus from the vagina. It may be present in very young women.

os uteri

The mouth of the uterus. It opens into the vagina.

os uteri externum

The opening of the cervical canal of the uterus into the vagina.

os uteri internum

The internal opening of the cervical canal into the uterus.

os ventriculi

The cardia of the stomach.