| submental triangle | A triangle bounded by the anterior belly of the digastric muscles, and the hyoid bone; the mylohyoid muscle forms its floor. Synonym: trigonum submentale. (05 Mar 2000) |
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| suboccipital triangle | A deep triangle bounded by the obliquus capitis inferior, the obliquus capitis superior, and the rectus capitis posterior major muscles. (05 Mar 2000) |
| superior carotid triangle | A space bounded by the superior belly of the omohyoid muscle, anterior border of the sternocleidomastoid, and posterior belly of the digastric; it contains the bifurcation of the common carotid artery. Synonym: trigonum caroticum, fossa carotica, Gerdy's hyoid fossa, Malgaigne's fossa, Malgaigne's triangle, superior carotid triangle. (05 Mar 2000) |
| superior triangle sign | In chest radiology, widening of the superior mediastinum, usually on the right, associated with collapse of the lower lobe producing traction on the mediastinal pleura. (05 Mar 2000) |
| supraclavicular triangle | 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) |
| suprameatal triangle | A triangle formed by the root of the zygomatic arch, the posterior wall of the bony external acoustic meatus, and an imaginary line connecting the extremities of the first two lines; used as a guide in mastoid operations. Synonym: Macewen's triangle. (05 Mar 2000) |
| deltoideopectoral triangle | A triangular depression bounded by the clavicle and the adjacent borders of the deltoid and pectoralis major muscles. Synonym: fossa infraclavicularis, deltoideopectoral triangle, deltoideopectoral trigone, infraclavicular triangle, Mohrenheim's fossa, Mohrenheim's space, regio infraclavicularis, trigonum deltoideopectorale. (05 Mar 2000) |
| digastric triangle | 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) |
| iliofemoral triangle | In fracture of the neck of the femur to determine upward displacement of the trochanter, lines are drawn on the body to form a triangle: line a is drawn around the body at the level of the anterior superior iliac spines; line b, perpendicular to line a, is drawn to the great trochanter of the femur; line c is drawn from the trochanter to the iliac spine; upward displacement is measured along line b. Synonym: iliofemoral triangle. (05 Mar 2000) |
| inferior carotid triangle | 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) |
| inferior occipital triangle | A triangle with its apex at the external occipital protuberance; its base is formed by a line joining the two mastoid processes. (05 Mar 2000) |
| inferior triangle sign | In chest radiology, lateral displacement of the diaphragmatic pleura near the diaphragm, associated with collapse of the upper lobe, usually on the right side. (05 Mar 2000) |
| infraclavicular triangle | A triangular depression bounded by the clavicle and the adjacent borders of the deltoid and pectoralis major muscles. Synonym: fossa infraclavicularis, deltoideopectoral triangle, deltoideopectoral trigone, infraclavicular triangle, Mohrenheim's fossa, Mohrenheim's space, regio infraclavicularis, trigonum deltoideopectorale. (05 Mar 2000) |
| inguinal triangle | 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) |
| interscalene triangle | Triangular gap bounded by the scalenus anterior and scalenus medius muscles and the first rib to which the muscles attach; the hiatus provides passage for the subclavian artery and the roots of the brachial plexus. Compression of the structures passing through the hiatus by any means is manifest as "thoracic outlet syndrome." Synonym: interscalene triangle. (05 Mar 2000) |