triangle

(tri'ang-gl) [L. iriangulum; tri-, three, + angulus, angle.] i. geometrical figure having three straight lines, joined two by two, forming three angles; trigone, z. In anatomy and surgery, a more or le triangular area bounded by muscles, bony prominences, or other structures, within which are normally found certain important nerves or blood-ve els; for these various triangles (Petit's, Scarpa's, etc.) see the proper names, ante'rior t., a large t. in the neck, bounded by the mandible above, the sternocleidomastoid muscle, and the midline of the neck anteriorly; it is subdivided into the inferior and superior carotid triangle and the submandibular t. auric'ular t., a t. formed by the base of the auricle and by lines drawn from the true tip of the auricle to the extremities of the base, ax'illary t., a triangular area embracing the inner aspect of the arm, the axilla, and the pectoral region which is one of the seats of predilection for the petechial initial rash of smallpox. car"diohepat'ic t., an area in' the fifth intercostal space on the right side, marking the interval between the heart and the liver, carot'id t., see inferior carotid t., and superior carotid t. cephal'ic t., a t. on the craniixm formed by lines connecting the me top i on, the mental point, and the occipital point, cru'ral t., an area of predilection for the petechial initial rash of smallpox; it occupies the lower abdominal, inguinal, and genital regions and the inner aspects of the thighs, the base of the triangle traversing the umbilicus, dig as'tric t., submandibular t. fa'cial t., a t. formed by lines connecting the basion, the alveolar point, and the nasal point. fem'oral t., Scarpa's* t. frontal t., a t. bounded above by the maximum frontal diameter and laterally by lines joining the extremities of this diameter with the glabella, iliofem'oral t., Bryant's* t. infe'rior carot'id t., bounded by the stemomastoid behind, the anterior belly of