| olfactory sulcus of nasal cavity | The narrow groove in the nasal cavity above the agger nasi that leads from the atrium to the olfactory area. Synonym: sulcus olfactorius cavum nasi. (05 Mar 2000) |
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| olfactory trigone | A grayish triangular area corresponding to the attachment of the olfactory peduncle ("olfactory nerve" or olfactory tract) to the base of the brain, at the anterior border of the anterior perforated substance. Synonym: trigonum olfactorium. (05 Mar 2000) |
| olfactory tubercle | A small, oval area at the base of the cerebral hemisphere, between the diverging medial and lateral olfactory striae, in the anteromedial part of the anterior perforated substance; it is formed by a small area of allocortex characterised by the presence of the islands of Calleja. Corresponding to a much more prominent structure in nonprimate mammals (especially rodents and insectivores), the olfactory tubercle receives fibres from the olfactory bulb by way of the intermediate olfactory stria; it has efferent connections with the hypothalamus and the mediodorsal nucleus of the thalamus. Synonym: tuberculum olfactorium. (05 Mar 2000) |
| alimentary tract | The passage leading from the mouth to the anus through the pharynx, oesophagus, stomach, and intestine. Synonym: alimentary canal, alimentary tract, digestive tube, tubus digestorius. (05 Mar 2000) |
| alimentary tract smear | A group of cytologic specimens containing material from the mouth (oral smear), oesophagus and stomach (gastric smear), duodenum (paraduodenal smear), and colon, obtained by specialised lavage techniques; used principally for the diagnosis of cancer of those areas. (05 Mar 2000) |
| anterior corticospinal tract | Uncrossed fibres forming a small bundle in the pyramidal tract. See: pyramidal tract. Synonym: tractus corticospinalis anterior, tractus pyramidalis anterior, anterior corticospinal tract, anterior pyramidal fasciculus, direct pyramidal tract, fasciculus corticospinalis anterior, fasciculus pyramidalis anterior, Turck's bundle, Turck's column, Turck's tract. (05 Mar 2000) |
| anterior pyramidal tract | Uncrossed fibres forming a small bundle in the pyramidal tract. See: pyramidal tract. Synonym: tractus corticospinalis anterior, tractus pyramidalis anterior, anterior corticospinal tract, anterior pyramidal fasciculus, direct pyramidal tract, fasciculus corticospinalis anterior, fasciculus pyramidalis anterior, Turck's bundle, Turck's column, Turck's tract. (05 Mar 2000) |
| anterior spinocerebellar tract | A bundle of fibres originating in the base of the posterior horn and zona intermedia throughout lumbosacral segments of the spinal cord, crossing to the opposite side and ascending in a peripheral position in the ventral half of the lateral funiculus. In its ascent through the rhombencephalon, the tract curves sharply dorsalward along the rostral border of the trigeminal motor nucleus, entering the cerebellum in a caudal direction over the dorsal surface of the superior cerebellar peduncle, and terminating as mossy fibres in the granular layer of the cortex of the cerebellar vermis. The bundle conveys proprioceptive and exteroceptive information largely from the opposite lower extremity. Synonym: tractus spinocerebellaris anterior, Gowers' column, Gowers' tract, ventral spinocerebellar tract. (05 Mar 2000) |
| anterior spinothalamic tract | The more anterior or ventral part of the spinothalamic tract that is involved in tactile sensation. See: spinothalamic tract. Synonym: tractus spinothalamicus anterior, ventral spinothalamic tract. (05 Mar 2000) |
| Arnold's tract | A fibre group originating in the cerebral cortex of the temporal lobe, particularly the superior and middle temporal gyri, following the sublenticular limb of the internal capsule into the lateral margin of the crus cerebri in which it descends to its termination in the pontine nuclei or the ventral part of the pons. Synonym: tractus temporopontinus, Arnold's bundle, Arnold's tract. (05 Mar 2000) |
| association tract | See: association system. (05 Mar 2000) |
| auditory tract | A bundle of ascending fibres that originate from the cochlear and auditory relay nuclei of the rhombencephalon, enter the trapezoid body, a transverse fibre stratum in which about half their number decussate, and from here turn rostrally along the lateral side of the spinothalamic tract; in the midbrain, it arches dorsally and enters the inferior colliculus in which all of its fibres terminate; the auditory pathway is transsynaptically extended from here by the brachium of the inferior colliculus to the medial geniculate body of the thalamus, from which in turn the auditory radiation leads to the auditory cortex; intercalated in the trapezoid body and along the ascending trajectory of the lemniscus are several cell groups in which part of the fibres synapse. Synonym: lemniscus lateralis, acoustic lemniscus, auditory lemniscus, auditory tract, lateral fillet. (05 Mar 2000) |
| benign mesothelioma of genital tract | A small, circumscribed, benign tumour of the genital tract, composed of small glandlike spaces lined by flattened or cuboidal mesothelium-like cells. (12 Dec 1998) |
| biliary tract | <anatomy> The biliary tract refers to the bile ducts within the liver, the common bile duct (connecting the liver and gallbladder to the small intestine) and the cystic duct (short duct that connects the common bile duct to the gallbladder). Blockage in any location in the biliary tract can result in obstructive jaundice. (27 Sep 1997) |
| biliary tract surgical procedures | Any surgical procedure performed on the biliary tract. (12 Dec 1998) |