| sternocostal triangle | A muscular defect in the diaphragm between the costal and the sternal portions. Synonym: Larrey's cleft, sternocostal triangle. (05 Mar 2000) |
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| subclavian 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) |
| subinguinal triangle | A triangular space at the upper part of the thigh, bounded by the sartorius and adductor longus muscles and the inguinal ligament, with a floor formed laterally by the iliopsoas muscle and medially by the pectineus muscle; the branches of the femoral nerve are distributed within the femoral triangle; it is bisected by the femoral vessels, which enter the adductor canal at its apex. Synonym: trigonum femorale, fossa scarpae major, Scarpa's triangle, subinguinal triangle. (05 Mar 2000) |
| submandibular 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) |
| submaxillary 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) |
| 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) |
| 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) |