‖ ostium
(ˈɒstɪəm)
Pl. ostia.
[L. ostium door, entrance, mouth of a river.]
† 1. The mouth of a river. Obs.
| 1665 Sir T. Herbert Trav. (1677) 89 The great and noble River Ganges in two Ostiums falls under 23 deg. 1695 Woodward Nat. Hist. Earth i. 43 Mud being reposed..near the Ostia of those Rivers. |
2. Anat. Applied to various orifices and openings of vessels in the animal body, e.g. those of the ventricles and pulmonary arteries, the Fallopian and Eustachian tubes, the urethra, etc. Also, a slit-like valve in an insect's heart. Also in combs. with mod.L. adjs.
| 1828 J. Quain Elem. Anat. viii. 537 The fimbriated border presents a fissure or opening, (ostium abdominale) into which the impregnated ovum is received at the moment of its liberation from the ovarium, and thence conveyed along the tube, which opens into the uterus by another aperture, (ostium uterinum). 1874 J. Hinton tr. von Tröltsch's Surg. Dis. Ear v. 36 The tympanic opening of the [Eustachian] tube (ostium tympanicum) lies directly opposite the irregularly shaped entrances to the mastoid cells. 1877 Huxley Anat. Inv. Anim. vii. 434 The margins of the ostia may be simple or may be produced inwards into folds which play the part of valves. 1878 Bell tr. Gegenbaur's Comp. Anat. 51 It is only when valves appear at the ostia of the cardiac tube, that the direction of the flow is defined. 1898 Allbutt's Syst. Med. V. 703 Close to the ostium [of the cardiac pulmonary valves]. 1909 Bailey & Miller Text-bk. Embryol. x. 232 The valves between the atrium and ventricle..develop for the most part from the walls of the triangular atrio-ventricular opening (ostium atrio-ventriculare). 1925 A. D. Imms Gen. Textbk. Entomol. 123 The blood enters the heart through lateral inlets or ostia, a pair of which is situated at each constriction between adjacent chambers. 1951 C. K. Weichert Anat. Chordates viii. 321 The ovum then passes through the ostium tubae into the Fallopian tube. 1962 W. H. Hollinshead Textbk. Anat. xix. 581/1 The atrium opens into the right ventricle by way of the right atrioventricular ostium. 1969 R. F. Chapman Insects xxxii. 661 The anterior and posterior lips of each ostium are reflexed into the heart so that they form a valve permitting the flow of blood into the heart.., but preventing its outward passage. Ibid. 663 There are unpaired excurrent ostia in the heart of Plecoptera and Embioptera. |