| horizontal atrophy | A progressive loss of alveolar and supporting bone surrounding the teeth, beginning at the most coronal level of the bone. Synonym: horizontal resorption. (05 Mar 2000) |
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| horizontal beam film | A radiograph made with the central axis of the X-ray beam parallel to the floor, able to show an air-fluid level. (05 Mar 2000) |
| horizontal cell | A type of nonspiking interneuron found in the retina, named for its morphology. Horizontal cells process the information from a large number of photoreceptors and synapse onto ganglion cells and other cell types in the retina. (18 Nov 1997) |
| horizontal cell of Cajal | A small fusiform cell found in the superficial layer of the cerebral cortex with its long axis placed horizontally. Synonym: Cajal's cell. (05 Mar 2000) |
| horizontal cells of retina | Cell's in the outer part of the inner nuclear layer of the retina that lie with their axes more or less parallel with the surface. They are thought to connect the rods of one part of the retina with cones of another part. (05 Mar 2000) |
| horizontal classification | <zoology> Classification which stresses grouping together taxa in a similar stage of evolution, rather than location on the same phyletic line. See: Vertical classification. (09 Jan 1998) |
| horizontal fissure of cerebellum | Horizontal fissure that divides the ansiform lobule into its major parts, crus I (superior semilunar lobule) and crus II (inferior semilunar lobule). Synonym: fissura horizontalis cerebelli, great horizontal fissure. (05 Mar 2000) |
| horizontal fissure of right lung | The deep fissure that separates the upper and middle lobes of the right lung. Synonym: fissura horizontalis pulmonis dextri, horizontal fissure of right lung, minor fissure. (05 Mar 2000) |
| horizontal fracture | A fracture of the facial bones in which there is a horizontal fracture at the base of the maxillae above the apices of the teeth. Synonym: horizontal fracture, Le Fort I fracture. (05 Mar 2000) |
| horizontal growth phase | An early stage of development of cutaneous melanoma by intraepidermal spread of atypical melanocytes. (05 Mar 2000) |
| horizontal osteotomy | An osteotomy performed intraorally for genioplasty; the inferior aspect of the anterior mandible is advanced or retruded by movement of the free segment. (05 Mar 2000) |
| horizontal overlap | The projection of the upper anterior and/or posterior teeth beyond their antagonists in a horizontal direction. Synonym: overjet, overjut. (05 Mar 2000) |
| horizontal part of duodenum | pars horizontalis duodeni, inferior part of duodenum, pars inferior duodeni |
| horizontal part of facial canal | First portion of facial canal, between beginning of canal (at the introitus of the facial canal at the end of the internal auditory meatus) and the point at which it turns to descend, beginning the descending part. There are two components (crura) of the horizontal part: the medially-located, anteriorly-directed medial crus and the laterally-placed, posteriorly-directed lateral crus, the two being continuous at a sharp bend, the genu of the facial canal. This lateral part is where the genicular ganglion is located and which communicates with the middle cranial fossa via the hiatus of the facial canal, through which the greater superficial petrosal nerve passes. (05 Mar 2000) |
| horizontal plane | A plane across the body at right angles to the coronal and sagittal plane's. Synonym: horizontal plane. (05 Mar 2000) |