| trigonum habenulae | A small triangular area on the dorsomedial surface of the thalamus at the caudal end of the medullary stria, corresponding to the underlying habenula. Synonym: trigonum habenulae, trigone of habenula. (05 Mar 2000) |
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| trigonum hypoglossi | A slight elevation in the floor of the inferior recess of the fourth ventricle, beneath which is the nucleus of origin of the twelfth cranial nerve. Synonym: trigonum nervi hypoglossi, eminentia hypoglossi, hypoglossal eminence, trigone of hypoglossal nerve, trigonum hypoglossi, tuberculum hypoglossi. (05 Mar 2000) |
| trigonum inguinale | The triangular area in the lower abdominal wall bounded by the inguinal ligament below, the border of the rectus abdominis medially and the inferior epigastric vessels (lateral umbilical fold) laterally. It is the site of direct inguinal hernia. Synonym: trigonum inguinale, Hesselbach's triangle, inguinal trigone. (05 Mar 2000) |
| trigonum lemnisci | A triangular area on the lateral surface of the caudal half of the mesencephalon, bordered caudally by the slight prominence of the lateral lemniscus, dorsally by the base of the inferior colliculus and the brachium of the superior colliculus, and ventrally by the crus cerebri. Synonym: Reil's triangle, triangle of fillet, trigone of fillet, trigonum lemnisci. (05 Mar 2000) |
| trigonum lumbale | An area in the posterior abdominal wall bounded by the edges of the latissimus dorsi and external oblique muscles and the iliac crest; herniations occasionally occur here. Synonym: trigonum lumbale, Petit's lumbar triangle. (05 Mar 2000) |
| trigonum lumbocostale | A triangular area in the diaphragm near the lateral arcuate ligament that is devoid of muscle fibres; it is covered by pleura superiorly and by peritoneum inferiorly. Synonym: Bochdalek's gap, trigonum lumbocostale. (05 Mar 2000) |
| trigonum musculare | The triangle bounded by the sternocleidomastoid muscle, the superior belly of the omohyoid muscle, and the anterior midline of the neck; the infrahyoid muscles occupy most of it. Synonym: trigonum musculare, trigonum omotracheale, inferior carotid triangle, omotracheal triangle, tracheal triangle. (05 Mar 2000) |
| trigonum nervi hypoglossi | A slight elevation in the floor of the inferior recess of the fourth ventricle, beneath which is the nucleus of origin of the twelfth cranial nerve. Synonym: trigonum nervi hypoglossi, eminentia hypoglossi, hypoglossal eminence, trigone of hypoglossal nerve, trigonum hypoglossi, tuberculum hypoglossi. (05 Mar 2000) |
| trigonum nervi vagi | A prominence in the floor of the inferior fovea of the fourth ventricle that overlies the dorsal motor nucleus of the vagus. Synonym: trigonum nervi vagi, ala cinerea, ashen wing, gray wing, trigone of vagus nerve, va'gi eminentia. (05 Mar 2000) |
| trigonum olfactorium | 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) |
| trigonum omoclaviculare | The triangle bounded by the clavicle, the omohyoid muscle, and the sternocleidomastoid muscle; it contains the subclavian artery and vein. Synonym: fossa supraclavicularis major, trigonum omoclaviculare, greater supraclavicular fossa, omoclavicular triangle, subclavian triangle. (05 Mar 2000) |
| trigonum omotracheale | An alternate term for muscular triangle. (05 Mar 2000) |
| trigonum palati | A triangular area bounded by the greatest transverse diameter of the palate and by lines converging from its extremities to the alveolar point. Synonym: trigonum palati. (05 Mar 2000) |
| trigonum sternocostale | A muscular defect in the diaphragm between the costal and the sternal portions. Synonym: Larrey's cleft, sternocostal triangle. (05 Mar 2000) |
| trigonum submandibulare | The triangle of the neck bounded by the mandible and the two bellies of the digastric muscle; it contains the submandibular gland. Synonym: trigonum submandibulare, digastric triangle, submaxillary triangle. (05 Mar 2000) |