Ostium

An ostium (: ostia) in anatomy is a small opening or orifice.

Ostium or ostia may refer to:

Human anatomy

 * Ostium of fallopian tube
 * Ostium of the uterus (disambiguation)
 * Ostium primum of the developing heart
 * Ostium secundum (foramen ovale) of the developing heart
 * Ostium maxillare of the maxillary sinus
 * Ostium vaginae (vaginal orifice)
 * Coronary ostium – opening of coronary arteries at root of aorta, superior to aortic valve
 * Sinus ostium an opening that connects a sinus to the nasal cavity itself.

In other animals

 * Ostium (sponges), the pores of living sponges
 * Ostia of female lepidoptera genitalia