- 1. An inlet or entrance to a cavity or channel. in anatomy, an open gap or hole. SEE ALSO: fossa, ostium, orifice, pore. 2. The diameter of the objective of a microscope. SYN: aditus [TA], apertura [TA]. [L. apertura, an opening]- angular a. the angle, in air, of light that passes from the object to the ends of the diameter of the front lens of the microscope objective.- inferior thoracic a. [TA] the inferior boundary of the bony thorax composed of the twelfth thoracic vertebra and the lower margins of the rib cage and sternum. SYN: apertura thoracis inferior [TA], thoracic outlet (1).- lateral a. of fourth ventricle [TA] one of the two lateral openings of the fourth ventricle into the subarachnoid space (the lateral cerebellomedullary cistern) at the cerebellopontine angle. SYN: apertura lateralis ventriculi quarti [TA], foramen lateralis ventriculi quarti, foramen of Key-Retzius, foramen of Luschka, foramen of Retzius.- median a. of fourth ventricle [TA] the large midline opening in the posterior inferior part of the roof of the fourth ventricle, connecting the ventricle with the posterior cerebellomedullary cistern. SYN: apertura mediana ventriculi quarti [TA], arachnoid foramen, foramen of Magendie.- numerical a. (N.A.) defined by the formula n sine a, where n is the refractive index of the medium between the object and objective lens and a is the angle between the central and the marginal ray entering the objective.- piriform a. [TA] the anterior nasal opening in the skull. SYN: apertura piriformis [TA], piriform opening.- superior thoracic a. [TA] the upper boundary of the bony thorax composed of the first thoracic vertebra and the upper margins of the first ribs and manubrium of the sternum. Note: clinicians refer to the superior thoracic a. as the “thoracic outlet.” as in “thoracic outlet syndrome.” SYN: apertura thoracis superior [TA], thoracic inlet, thoracic outlet (2).- tympanic a. of canaliculus for chorda tympani [TA] the small canal opening found lateral to the pyramidal eminence in the posterior wall of the middle ear cavity from which the chorda tympani nerve emerges to pass anteriorly between the ossicles accompanied by a branch of the stylomastoid artery. SYN: apertura tympanica canaliculi chordae tympani [TA], tympanic opening of canaliculus for chorda tympani.
* * *1) an opening or open space2) the diameter of the stop in an optical system that determines the diameter of the bundle of rays traversing the instrument
* * *ap·er·ture (apґər-chər) [L. apertura, q.v.] 1. an opening, or orifice; see also apertura. 2. the diameter of a microscope objective lens or the (adjustable) diameter of the iris diaphragm of a camera lens.
Medical dictionary. 2011.