| electrical axis | The net direction of the electromotive forces developed in the heart during its activation, usually represented in the frontal plane. See: triaxial reference system. (05 Mar 2000) |
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| electron optical axis | <physics> The path of an electron through an electron optical system along which it suffers no deflection due to lens fields. This axis does not necessarily coincide with the mechanical axis of the system. (05 Aug 1998) |
| embryonic axis | The cephalocaudal axis established in the embryo by the primitive streak. (05 Mar 2000) |
| encephalomyelonic axis | The central nervous system; the brain and spinal cord. Synonym: encephalomyelonic axis, neural axis. (05 Mar 2000) |
| transporionic axis | An imaginary line connecting the upper central points of the external auditory meatuses; used in radiographic cephalometry. See: porion. (05 Mar 2000) |
| transverse horizontal axis | An imaginary line around which the mandible may rotate through the horizontal plane. Synonym: hinge axis, mandibular axis. (05 Mar 2000) |
| external axis of eye | That part of the optic axis from the midpoint of anterior surface of the cornea to the posterior surface of the posterior pole of the external surface of the sclera. Synonym: axis bulbi externus. (05 Mar 2000) |
| facial axis | A line drawn from the subnasal point to the midpoint of the sphenoethmoidal suture. Synonym: facial axis. (05 Mar 2000) |
| Y-axis | A cephalometric indicator of the vertical and horizontal coordinates of mandibular growth expressed in degrees of the inferior facial angle formed by the intersection of the sella-gnathion plane with the Frankfort horizontal plane. (05 Mar 2000) |
| left axis deviation | A mean electrical axis of the heart pointing to -30 |
| long axis | A line extending through the centre of an object lengthwise; in dentistry, the line extending inciso-(occluso-) cervically parallel to axial surfaces of a tooth. (05 Mar 2000) |
| long axis of body | long axis of body |
| long axis view | In echocardiography, a projection parallel to the interventricular septum of the heart; four-chamber view. (05 Mar 2000) |