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triangle (trI´ang-gl)

In anatomy and surgery, a three-sided area with arbitrary or natural boundaries. See also trigonum. [L. triangulum, fr. tri-, three, + angulus, angle]
anal t. the posterior portion of the perineal region through which the anal canal opens; bounded by a line through both isehial tuberosities, the sacrotuberous ligaments and the coccyx.regio analis [NA], anal region;
anterior t. of neck the area of the neck bounded by the mandible, the anterior border of the sternocleidomastoid muscle, and the anterior midline of the neck; it is subdivided into carotid, muscular, submandibular, and submental t.'s.anterior region of neck, regio cervicalis anterior, trigonum cervicale anterius;
Assézat's t. a t. formed by lines connecting the nasion with the alveolar and nasal point; used to indicate prognathism in comparative craniology.
auricular 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.
t. of auscultation space bounded by the lower border of the trapezius, the latissimus dorsi, and the medial margin of the scapula, where the absence of musculature allows respiratory sounds to be heard clearly with a stethoscope.
axillary t. a triangular area embracing the medial 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.
Béclard's t. area bounded by the posterior border of the hyoglossus muscle, the posterior belly of the digastric and the greater horn of the hyoid bone.
Bonwill t. an equilateral t. formed by lines from the contact points of the lower central incisors, or the medial line of the residual ridge of the mandible, to the condyle on either side and from one condyle to the other.
Bryant's t. in fracture of the neck of the femur to determine upward displacement of the trochanter, lines are drawn on the body to form a t.: 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.iliofemoral t;
Burger's t. a scalene t. representing the frontal plane electrocardiographic leads comparable to but more accurate than Einthoven's t. See Einthoven's t.
Burow's t. a t. of skin and subcutaneous fat excised so that a pedicle flap can be advanced without buckling the adjacent tissue.
Calot's t. t. bounded by the cystic artery, cystic duct, and hepatic duct; its dissection early in cholecystectomy safeguards essential structures, should there be anatomic variations from the norm.
cardiohepatic t. cardiohepatic angle
carotid t. 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.trigonum caroticum [NA], fossa carotica, Gerdy's hyoid fossa, Malgaigne's fossa, Malgaigne's t., superior carotid t;
cephalic t. a t. on the cranium formed by lines connecting the metopion, the pogonion, and the occipital point.
cervical t. any of the t.'s of the neck.
Codman's t. in radiology, the interface between growing bone tumor and normal bone, presenting as an incomplete triangle formed by periosteum.
crural 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 t. traversing the umbilicus.
deltoideopectoral t. infraclavicular fossa
digastric t. submandibular t
Einthoven's t. an imaginary equilateral t. with the heart at its center, its equal sides representing the three standard limb leads of the electrocardiogram.
Elaut's t. t. formed by the iliac arteries and the promontory of the sacrum.
t. of elbow cubital fossa
facial t. a t. formed by lines connecting the basion, the prosthion, and the nasion.
Farabeuf's t. the t. formed by the internal jugular and facial veins and the hypoglossal nerve.
femoral t. 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 t.; it is bisected by the femoral vessels, which enter the adductor canal at its apex.trigonum femorale [NA], fossa scarpae major, Scarpa's t., subinguinal t;
t. of fillet lemniscal trigone
frontal t. a t. bounded above by the maximum frontal diameter and laterally by lines joining the extremities of this diameter with the glabella.
Garland's t. a triangular area of relative resonance in the lower back near the spine, found in the same side as a pleural effusion.
Gombault's t. See semilunar fasciculus.
Grocco's t. a triangular patch of dullness at the base of the chest alongside the spinal column, on the side opposite a pleural effusion.paravertebral t;
Grynfeltt's t. a triangular space bounded above by the end of the last rib and the serratus posterior inferior muscle, anteriorly by the internal oblique, and posteriorly by the quadratus lumborum; lumbar hernia occurs in this space.Lesshaft's t;
Hesselbach's t. inguinal t
iliofemoral t. Bryant's t
inferior carotid t. muscular t
inferior occipital t. a t. with its apex at the external occipital protuberance; its base is formed by a line joining the two mastoid processes.
infraclavicular t. infraclavicular fossa
inguinal t. 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.trigonum inguinale [NA], Hesselbach's t., inguinal trigone;
interscalene t. scalene hiatus
Killian's t. the triangular-shaped area of the cervical esophagus bordered by the oblique fibers of the inferior constrictor muscle of the pharynx and the transverse fibers of the cricopharyngeus muscle through which Zenker's diverticulum occurs, and the A-V nodal triangle between the coronary sinus orifice and the ventricular crest.laimer t;
Koch's t. a triangular area of the wall of the right atrium of the heart, that marks the situation of the atrioventricular node.
Labbé's t. an area bounded below by a horizontal line touching the lower edge of the cartilage of the left ninth rib, laterally by the line of the false ribs, and to the right side by the liver; here the stomach is normally in contact with the abdominal wall.
laimer t. Killian's t
Langenbeck's t. a t. formed by lines drawn from the anterior superior iliac spine to the surface of the great trochanter and to the surgical neck of the femur; a penetrating wound in this area probably involves the joint.
Lesser's t. the space between the bellies of the digastric muscle and the hypoglossal nerve.
Lesshaft's t. Grynfeltt's t
Lieutaud's t. trigone of bladder
lumbar t. 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.trigonum lumbale [NA], Petit's lumbar t;
lumbocostoabdominal t. an irregular area bounded by the serratus posterior inferior, obliquus externus, obliquus internus, and erector spinae muscles.
Macewen's t. suprameatal t
Malgaigne's t. carotid t
Marcille's t. an area bounded by the medial border of the psoas major, the lateral margin of the vertebral column, and the iliolumbar ligament below; it is crossed by the obturator nerve.
muscular t. the t. 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.trigonum musculare [NA], trigonum omotracheale [NA], inferior carotid t., omotracheal t., tracheal t;
occipital t. a t. of the neck bounded by the trapezius, the sternocleidomastoid, and the omohyoid muscles. See also inferior occipital t.
omoclavicular t. supraclavicular t
omotracheal t. muscular t
palatal t. a triangular area bounded by the greatest transverse diameter of the palate and by lines converging from its extremities to the alveolar point.trigonum palati;
paravertebral t. Grocco's t
Petit's lumbar t. lumbar t
Philippe's t. See semilunar fasciculus.
Pirogoff's t. a t. formed by the intermediate tendon of the digastric muscle, the posterior border of the mylohyoid muscle, and the hypoglossal nerve.
posterior t. of neck the region of the neck bounded by the sternocleidomastoid muscle, the trapezius muscle, and the upper border of the clavicle, including the omoclavicular triangle.lateral region of neck, regio cervicalis lateralis, trigonum cervicale posterius;
pubourethral t. a t. in the perineum bounded by the transversus perinei, the ischiocavernosus, and the bulbocavernosus muscles.
Reil's t. lemniscal trigone
sacral t. the surface area over the sacrum.
t. of safety the area at the lower left sternal border where the pericardium is not covered by lung (pericardial notch); preferred site for aspiration of pericardial fluid.
Scarpa's t. femoral t
sternocostal t. trigonum sternocostale
subclavian t. supraclavicular t
subinguinal t. femoral t
submandibular t. the t. of the neck bounded by the mandible and the two bellies of the digastric muscle; it contains the submandibular gland.trigonum submandibulare [NA], digastric t., submaxillary t;
submaxillary t. submandibular t
submental t. a t. bounded by the anterior belly of the digastric muscles, and the hyoid bone; the mylohyoid muscle forms its floor.trigonum submentale [NA];
suboccipital t. a deep t. bounded by the obliquus capitis inferior, the obliquus capitis superior, and the rectus capitis posterior major muscles.
superior carotid t. carotid t
supraclavicular t. the t. bounded by the clavicle, the omohyoid muscle, and the sternocleidomastoid muscle; it contains the subclavian artery and vein.fossa supraclavicularis major [NA], trigonum omoclaviculare [NA], greater supraclavicular fossa, omoclavicular t., subclavian t;
suprameatal t. a t. 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.Macewen's t;
tracheal t. muscular t
Tweed t. a t. defined by facial and dental landmarks on a lateral cephalometric film, using the Frankfort horizontal plane as a base and intended for use as a guide in the evaluation and planning of orthodontic treatment.
umbilicomammillary t. a t. with its apex at the umbilicus and its base at the line joining the nipples.
urogenital t. the anterior portion of the perineal region containing the openings of the urethra and vagina in the female and the urethra and root structures of the penis in the male.regio urogenitalis [NA], urogenital region;
t. of vertebral artery triangular area in the root of the neck bounded laterally by the scalenus anterior and medially by the longus coli muscles; the two muscles meet at the triangle's apex, formed by the anterior (carotid) tubercle of the transverse process of vertebra C6; the vertebral artery arises from the subclavian artery at the base of the t., bisecting the t. as it ascends to the apex to enter the transverse foramen of vertebra C6.
vesical t. trigone of bladder
Ward's t. an area of diminished density in the trabecular pattern of the neck of the femur evident by x-ray as well as by direct inspection.
Weber's t. on the sole of the foot, an area indicated by the heads of the first and fifth metatarsal bone and the center of the plantar surface of the heel.
Wilde's t. pyramid of light


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