ostium, pi. os'tia

(os'tJ-um) [L. dim. of os, mouth.] A small opening, especially one of entrance into a hollow organ or canal, o. abdomina'le or 0. abdomina'le tu'bae uteri'nse [BNA], the fimbriated or ovarian extremity of an oviduct, o. arterio's um [BNA], arterial orifice, the opening from the ventricle of the heart into the aorta or the pulmonary artery. 0. a'trio-ventricula're, o. venosum. 0. inter'nujn, o. uterinum tubse, the uterine extremity of an oviduct, o. pharynge'um or o. pharynge'umtuTjseauditi'vaelBNA], pharyngeal opening of the auditory (Eustachian) tube, in the upper part of the nasopharynx about half an inch behind the posterior extremity of the inferior turbinal on each side. u. tympan'icum, or o. tympan'icum tu'bae audit i'vse [BNA], tympanic opening of the auditory (Eustachian) tube, in the anterior part of the tympanic cavity below the canal for the tensor tympani muscle, o. uteri'num tu'bae [BNA], the uterine opening of the oviduct. vagi 'use, the vulvar orifice of the vagina, o. veno 'sum [B NA], venous orifice, the communication between the auricle (atrium) and ventricle on either side of the heart.