| LAS | laboratory automation system; lateral amyotrophic sclerosis; laxative abuse syndrome; left anterior-... |
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| LASH | left anterior superior hemiblock |
| LSR | lanthanide shift reagent; lecithin/ sphingomyelin ratio; left superior rectus [muscle]; liver/spleen... |
| LSVC | left superior vena cava |
| MSO | management service organization; medial superior olive; medical staff organization |
| fissura mediana anterior medullae oblongatae | The longitudinal groove in the midline of the anterior aspect of the medulla oblongata; it is the medullary equivalent of the anterior median fissure of the spinal cord and ends at the foramen caecum posterius; its caudal part is obliterated by the decussation of the pyramids. Synonym: fissura mediana anterior medullae oblongatae, anteromedian groove. (05 Mar 2000) |
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| fissura mediana anterior medullae spinalis | A deep median fissure on the anterior surface of the spinal cord. Synonym: fissura mediana anterior medullae spinalis, anteromedian groove, sulcus ventralis. (05 Mar 2000) |
| fissura obliqua pulmonis | The deep fissure in each lung that runs obliquely downward and forward. It divides the upper and lower lobes of the left lung and separates the upper and middle lobes from the lower lobe of the right lung. Synonym: fissura obliqua pulmonis, major fissure, oblique fissure. (05 Mar 2000) |
| fissura parietooccipitalis | A very deep, almost vertically oriented fissure on the medial surface of the cerebral cortex, marking the border between the parietal lobe and the cuneus of the occipital lobe; its lower part curves forward and fuses with the anterior extent of the calcarine fissure (sulcus calcarinus); the great depth of this combined fissure causes a bulge in the medial wall of the occipital horn of the lateral ventricle, the calcar avis. Synonym: sulcus parieto-occipitalis, fissura parietooccipitalis, parieto-occipital fissure. (05 Mar 2000) |
| fissura petro-occipitalis | A fissure between the petrous part of the temporal bone and the basilar part of the occipital bone that extends anteromedially from the jugular foramen; includes the jugular foramem (at its posterior end). Synonym: fissura petro-occipitalis, Ecker's fissure. (05 Mar 2000) |
| fissura petrosquamosa | A shallow fissure indicating externally the line of fusion of the petrous and squamous portions of the temporal bone. Synonym: fissura petrosquamosa. (05 Mar 2000) |
| fissura petrotympanica | A fissure between the tympanic and petrous portions of the temporal bone; it transmits the chorda tympani nerve through a small patent portion, the anterior canaliculus of the chorda tympani. Synonym: fissura petrotympanica, glaserian fissure. (05 Mar 2000) |
| fissura posterolateralis | The earliest fissure to appear in the development of the cerebellum; it separates the flocculus and nodulus from the uvula and tonsil. Synonym: fissura posterolateralis, prenodular fissure. (05 Mar 2000) |
| fissura prima cerebelli | The deepest fissure of the cerebellum; demarcates the division of anterior and posterior lobes of the cerebellum; second to appear embryologically. Synonym: fissura prima cerebelli. (05 Mar 2000) |
| fissura pterygoidea | The cleft between the medial and lateral laminae of the pterygoid process of the sphenoid bone into which the pyramidal process of the palatine bone is fitted. Synonym: incisura pterygoidea, fissura pterygoidea, pterygoid notch. (05 Mar 2000) |
| fissura pterygomaxillaris | The narrow gap between the lateral pterygoid plate and the infratemporal surface of the maxilla through which the infratemporal fossa communicates with the pterygopalatine fossa; gives passage to the third part of the maxillary artery and the posterior superior alveolar arteries, veins and nerves. Synonym: fissura pterygomaxillaris, fissura pterygopalatina. (05 Mar 2000) |
| fissura pterygopalatina | The narrow gap between the lateral pterygoid plate and the infratemporal surface of the maxilla through which the infratemporal fossa communicates with the pterygopalatine fossa; gives passage to the third part of the maxillary artery and the posterior superior alveolar arteries, veins and nerves. Synonym: fissura pterygomaxillaris, fissura pterygopalatina. (05 Mar 2000) |
| fissura pudendi | The cleft between the labia majora. Synonym: rima pudendi, fissura pudendi, pudendal cleavage, pudendal slit, rima vulvae, urogenital cleft, vulvar slit. (05 Mar 2000) |
| fissura secunda cerebelli | A fissure that separates the uvula of the inferior vermis of the cerebellum from the pyramid. Synonym: fissura secunda cerebelli. (05 Mar 2000) |
| fissura sphenopetrosa | A narrow fissure between the undersurface of the greater wing of the sphenoid and the petrous portion of the temporal bone. Synonym: fissura sphenopetrosa. (05 Mar 2000) |