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Medical Dictionary


arabinoadenosine (a′ra-bin-o-ah-den′o-sen)
SYN: arabinosyladenine.

arabinocytidine (a′ra-bin-o-si′ti-den)
SYN: arabinosylcytosine.

arabinofuranosyladenine (a′ra-bin-o-foor′a-no-sil-ad′e-nen)
An arabinoside that has antiviral activity.

arabinofuranosylcytosine (a′ra-bin-o-foor′a-no-sil-si′to-sen)
SYN: arabinosylcytosine.

arabinose (Ara) (a-rab′i-nos, a′ra-bin-os)
A pentose; both of its enantiomers are widely distributed in plants, usually in complex polysaccharides; used in culture media. d-A. is an epimer of d-ribose. [arabin + -ose (1)] a. 5-phosphate a phosphorylated a. that is an intermediate in the pentose phosphate pathway. a. 5-phosphate 2-epimerase an enzyme in the pentose phosphate pathway that reversibly interconverts a. and ribose 5-phosphate.

arabinoside (a-rab′i-no-sid)
A ribonucleoside in which the sugar moiety is arabinose. It often has antibiotic activity.

arabinosis (a-rab-i-no′sis)
Disordered metabolism of arabinose.

arabinosuria (a-rab′i-no-soo′re-a)
Excretion of arabinose in the urine.

arabinosyladenine (a′ra-bin-o-sil-a′den-en)
Used for herpes simplex corneae and vaccinial keratitis. SYN: arabinoadenosine.

arabinosylcytosine (aC, araC) (a′ra-bin-o-sil-si′to-sen)
A compound of arabinose and cytosine, analogous to ribosylcytosine (cytidine), that inhibits the biosynthesis of DNA; used as a chemotherapeutic agent because of antiviral and tumor-growth-inhibiting properties. SYN: arabinocytidine, arabinofuranosylcytosine, cytarabine.

arabitol (a-rab′i-tol)
A sugar alcohol obtained from the reduction of arabinose.

Abbreviation for cytosine arabinoside.

Symbol for arabinosylcytosine.

arachic acid (a-rak′ik)
SYN: arachidic acid.

arachidic acid (a-ra-kid′ik)
A fatty acid contained in peanut oil, butter, and other fats. SYN: arachic acid, n-eicosanoic acid, n-icosanoic acid. [Arachis, fr. G. arakis, leguminous weed]

arachidonic acid (a-rak-i-don′ik)
5,8,11,14-Eicosatetraenoic (icosatetraenoic) acid;an unsaturated fatty acid, usually essential in nutrition; the biological precursor of the prostaglandins, the thromboxanes, and the leukotrienes (collectively known as eicosanoids).

arachidonic acid cascade
Eicosanoid synthetic pathway.

arachis oil (ar′a-kis)
SYN: peanut oil.

arachnephobia (a-rak-ne-fo′be-a)
Morbid fear of spiders. SYN: arachnophobia. [G. arachne, spider, + phobos, fear]

Arachnia (a-rak′ne-a)
A genus of nonmotile, nonsporeforming, facultatively anaerobic bacteria (family Actinomycetaceae) containing Gram-positive, non–acid-fast, branched, diphtheroid rods (0.2–0.3 by 3.0–5.0 μm and longer). These organisms produce filamentous microcolonies. Their metabolism is fermentative. Primarily propionic and acetic acids are produced from glucose. Catalase is not produced. The cell wall contains diaminopimelic acid but not arabinose. These organisms are pathogenic for humans, causing lacrimal canaliculitis and typical actinomycosis. The type species is A. propionica. A. propionica a species causing lacrimal canaliculitis and typical actinomycosis; it is the type species of the genus A.. SYN: Propionibacterium propionicus.

Arachnida (a-rak′ni-da)
A class of arthropods in the subphylum Chelicerata, consisting of spiders, scorpions, harvestmen, mites, ticks, and allies. [G. arachne, spider]

arachnidism (a-rak′ni-dizm)
Systemic poisoning following the bite of a spider (especially of the black widow). necrotic a. a. caused by spiders belonging to the genus Loxosceles; cutaneous necrosis develops at the bite site, with slow healing and possible disfigurement.

arachnodactyly (a-rak-no-dak′ti-le)
A condition in which the hands and fingers, and often the feet and toes, are abnormally long and slender; a characteristic of Marfan syndrome [MIM*154700], Achard syndrome [MIM*100700], the MASS syndrome [MIM*157700], and kindred hereditary disorders of connective tissue. SYN: spider finger. [G. arachne, spider, + daktylos, finger]

arachnoid (a-rak′noyd)
SYN: a. mater. [G. arachne, spider, cobweb, + eidos, resemblance] a. of brain SYN: cranial a. mater. cranial a. mater [TA] that portion of the a. that lies within the cranial cavity and surrounds the brain and the cranial portion of the subarachnoid space. In several sites it is relatively widely separated from the pia mater, creating the cranial subarachnoid cisterns. SEE ALSO: a. mater. SYN: arachnoidea mater cranialis [TA] , arachnoidea mater encephali&star, a. mater cranialis, a. mater encephali, a. of brain, cerebral part of a.. a. mater [TA] A delicate fibrous membrane forming the middle of the three coverings of the central nervous system. In life the a. (specifically the a. barrier cell layer) is tenuously attached to the externally adjacent dura mater (specifically the dural border cells) and there is no naturally occurring space at the dura-a. interface. Thus in a spinal puncture dura mater and a. are penetrated simultaneously as if a single layer. Separation of the a. mater from the dura mater (usually through the dural border cell layer) may result from traumatic or pathologic processes creating what is commonly, but incorrectly, called a subdural hematoma. The a. mater is named for the delicate, spider weblike filaments that extend from its deep surface, through the CSF of the subarachnoid space, to the pia mater. SEE ALSO: leptomeninx. SYN: arachnoidea mater, arachnoides [TA] , a. membrane, a., parietal layer of leptomeninges. a. mater cranialis SYN: cranial a. mater. a. mater encephali SYN: cranial a. mater. a. mater and pia mater a. of spinal cord SYN: spinal a. mater. spinal a. mater [TA] that portion of the a. that lies within the vertebral canal and surrounds the spinal cord and the vertebral portion of the subarachnoid space. It extends from the foramen magnum above to the S2 vertebral level. Since the spinal cord ends at the L2 vertebral level, a wide separation occurs between the a. and pia mater, the lumbar cistern, filled with cerebrospinal fluid in which the cauda equina is suspended. SYN: arachnoidea mater spinalis [TA] , a. of spinal cord, arachnoidea spinalis, spinal part of a.. arachnoidea spinalis SYN: spinal a. mater.

arachnoidal (a-rak-noy′dal)
Relating to the arachnoid membrane, or arachnoidea.

arachnoidea mater, arachnoides (a-rak-noyd′e-a, -dez) [TA]
SYN: arachnoid mater. [Mod. L. arachnoideus fr. G. arachne, spider, + eidos, resemblance] a. spinalis [TA] SYN: spinal arachnoid mater.

arachnoiditis (a-rak-noy-di′tis)
Inflammation of the arachnoid membrane often with involvement of the subjacent subarachnoid space. SEE ALSO: leptomeningitis. [arachnoidea + -itis, inflammation] adhesive a. thickening of the leptomeninges, sometimes with obliteration of the subarachnoid space; commonly related to acute or chronic leptomeningitis of bacterial or chemical origin. SEE ALSO: leptomeningeal fibrosis. SYN: obliterative a.. neoplastic a. SYN: neoplastic meningitis. obliterative a. SYN: adhesive a..

arachnolysin (a-rak-nol′i-sin)
A hemolytic substance in the venom of certain spiders.

arachnophobia (a-rak-no-fo′be-a)
SYN: arachnephobia.

aralkyl (a-ral′kil)
A radical in which an aryl group is substituted for a hydrogen atom of an alkyl group; e.g., C6H5CH2&cbond;. SYN: arylated alkyl.

François A., French physician, 1817–1861. See A.-Duchenne disease, Duchenne-A. disease.

araneism (a-ran′ism)
Rarely used term for arachnidism.

(Aranzio), Giulio C., Italian anatomist and physician, 1530–1589. See A. ligament, A. nodule, A. ventricle, corpus arantii, ductus venosus arantii.

araphia (a-ra′fe-a)
SYN: holorachischisis. [G. a- priv. + rhaphe, a seam]

arbor, pl .arbores (ar′bor, ar-bo′rez)
In anatomy, a treelike structure with branchings. [L. tree] a. vitae [TA] the arborescent appearance of gray and white matter in sagittal sections of the cerebellum. a. vitae uteri SYN: palmate folds of cervical canal, under fold.

arborescent (ar-bo-res′ent)
SYN: dendriform.

arborization (ar′bor-i-za′shun)
1. The terminal branching of nerve fibers or blood vessels in a branching treelike pattern. 2. The branched pattern formed under certain conditions by a dried smear of cervical mucus.

arborize (ar′bor-iz)
To spread in a treelike branching pattern.

arboroid (ar′bor-oyd)
Denoting a colony of protozoa, each of which remains attached to another cell or to the main stem at one point, forming a branching or dendritic figure. [L. arbor, tree, + G. eidos, resemblance]

arborvirus (ar′bor-vi′rus)
Obsolete term for arbovirus.

arbovirus (ar′bo-vi′rus)
An old name for a large, heterogeneous group of RNA viruses. There are over 500 species, which are distributed among several families (Togaviridae, Flaviviridae, Bunyaviridae, Arenaviridae, Rhabdoviridae, Reoviridae), and which have been recovered from arthropods, bats, and rodents; most, but not all, are arthropod-borne. These taxonomically diverse animal viruses are unified by an epidemiologic concept, i.e., transmission between vertebrate hosts by blood-feeding (hematophagous) arthropod vectors, such as mosquitoes, ticks, sandflies, and midges.. Although about 100 species can infect humans, in most instances diseases produced by these viruses are of a very mild nature and difficult to distinguish from illnesses caused by viruses of other taxonomic groups. Apparent infections may be separated into several clinical syndromes: undifferentiated type fevers (systemic febrile disease), hepatitis, hemorrhagic fevers, and encephalitides. [ar, arthropod, + bo, borne, + virus]

Abbreviation for AIDS-related complex.

arc (ark)
1. A curved line or segment of a circle. 2. Continuous luminous passage of an electric current in a gas or vacuum between two or more separated carbon or other electrodes. [L. arcus, a bow] auricular a., binauricular a. a line carried over the cranium from the center of one external auditory meatus to that of the other. SYN: interauricular a.. bregmatolambdoid a. the line running along the sagittal suture from the bregma to the apex of the lambdoid suture. crater a. an a. of a direct current that forms a pitlike excavation at the positive pole. flame a. an a. between two impregnated electrodes that causes volatilization of the core with resultant flame. interauricular a. SYN: auricular a.. longitudinal a. of skull the line carried over the skull in the midline from the nasion to the opisthion. mercury a. an electric discharge through mercury vapor between electrodes, one of which is usually mercury; provides a rich source of therapeutic ultraviolet rays; the containing tube is usually quartz; may also be glass with a fluorite window. nasobregmatic a. a line running through the midline of the forehead from the nasion to the bregma. naso-occipital a. the a. in the midline from the root of the nose to the inferior limit of the external occipital protuberance. pulmonary a. radiographically displayed contour of main pulmonary artery on frontal chest radiograph. reflex a. the route followed by nerve impulses in the production of a reflex act, from the peripheral receptor organ through the afferent nerve to the central nervous system synapse and then through the efferent nerve to the effector organ. Riolan a. 1. SYN: intestinal arterial arcades, under arcade. 2. SYN: marginal artery of colon. SEE ALSO: Riolan anastomosis. 3. SYN: Riolan anastomosis.

arcade (ar-kad)
An anatomic structure or structures (especially a blood vessel) taking the form of a series of arches. [L. arcus, arc, bow] anomalous mitral a. short chordae tendineae extending from both papillary muscles to the central portion of the anterior leaflet of the mitral valve and resulting in stenosis or incompetence of the valve. arterial arcades a series of anastomosing arterial arches, as the intestinal arterial arcades between the branches of the jejunal and ileal arteries in the mesentery and the pancreaticoduodenal arteries on the head of the pancreas. Flint a. a series of vascular arches at the bases of the pyramids of the kidney. intestinal arterial arcades the series of arterial arches formed in the mesentery by anastomoses between adjacent jejunal and ileal arteries and from which vasa recta arise. The arterial arcades of the ileum are shorter and more complex than those of the jejunum. SEE ALSO: arterial arches of ileum, under arch, arterial arches of jejunum, under arch, marginal artery of colon. SYN: intermesenteric arterial anastomoses, Riolan arc (1) , Riolan arcades. lower dental a. mandibular dental a.. mandibular dental a. [TA] the teeth supported by the alveolar part of the mandible, whether the 10 deciduous teeth or the 16 permanent teeth. SYN: arcus dentalis inferior&star, lower dental a.&star, inferior dental arch, mandibular dentition. marginal a. marginal artery of colon. maxillary dental a. [TA] the teeth supported by the alveolar process of the two maxillae, whether the 10 deciduous teeth or the 16 permanent teeth. SYN: arcus dentalis maxillaris [TA] , arcus dentalis superior&star, upper dental a.&star, maxillary dentition, superior dental arch. pancreaticoduodenal arterial arcades anastomoses between the anterior and posterior pancreaticoduodenal arteries (from the gastroduodenal artery) and the anterior and posterior inferior pancreaticoduodenal arteries (from the superior mesenteric artery) on the anterior and posterior aspects of the head of the pancreas and the duodenum, supplying both structures. Riolan arcades SYN: intestinal arterial arcades. SEE ALSO: Riolan anastomosis. upper dental a. maxillary dental a..

Arcanobacterium (ar-ka′no-bac-ter′e-um)
A genus of nonmotile, facultatively anaerobic bacteria containing Gram-positive slender irregular rods, sometimes showing clubbed ends that may be in V formation with no filaments. These organisms are obligate parasites of the pharynx in farm animals and humans, occasionally causing lesions on the pharynx or skin. The type species is A. haemolyticum. A. haemolyticum a species that causes pharyngitis and chronic skin ulcers in humans as well as farm animals.

arcate (ar′kat)
SYN: arcuate.

arch [TA]
Any structure resembling a bent bow or an a.; an arc. In anatomy, any vaulted or archlike structure. See arcus. SYN: arcus [TA] . [thru O. Fr. fr. L. arcus, bow] abdominothoracic a. a bell-shaped line defined by the lower end of the sternum and the costal arches on each side, constituting a boundary line between the anterolateral portions of the thoracic and abdominal walls. alveolar a. of mandible [TA] the free margin of the alveolar process of the mandible. SYN: arcus alveolaris mandibulae [TA] , limbus alveolaris (1) . alveolar a. of maxilla [TA] the free border of the alveolar process of the maxilla. SYN: arcus alveolaris maxillae [TA] , limbus alveolaris (2) . anterior a. of atlas [TA] an a. that connects the lateral masses of the atlas anteriorly and articulates with the anterior articular facet of the dens of the axis. SYN: arcus anterior atlantis [TA] . anterior palatine a. SYN: palatoglossal a.. a. of the aorta SYN: aortic a. (1) . aortic a. 1. the curved portion between the ascending and descending parts of the aorta; it begins as a continuation of the ascending aorta posterior to the sternal angle, runs posteriorly and slightly to the left as it passes over the root of the left lung, and becomes the descending aorta as it reaches and begins to course along the vertebral column; it gives rise to the brachiocephalic trunk, the left common carotid and left subclavian arteries; SYN: a. of the aorta. 2. any member of the several pairs of arterial channels encircling the embryonic pharynx in the mesenchyme of the brachial arches; there are potentially six pairs, but in mammals the fifth pair is poorly developed or absent. The first and second pairs are functional only in very young embryos; the third pair is involved in the formation of the carotids; the fourth a. on the left is incorporated in the a. of the aorta; the sixth pair forms the proximal part of the pulmonary arteries. SYN: arcus aortae. aortic arches a series of arterial channels encircling the embryonic pharynx in the mesenchyme of the branchial arches. There are potentially six pairs, but in mammals the fifth pair is poorly developed or absent. The first and second pairs are functional only in very young embryos; the third pair is involved in the formation of the carotids; the fourth a. on the left is incorporated in the a. of the aorta; the sixth pair forms the proximal part of the pulmonary arteries. arterial arches of colon anastomoses between adjacent branches of the colic arteries that form arches in the mesocolon from which the walls of the colon are supplied. When these form a continuous paracolic artery, it is referred to as the marginal artery of the colon. See marginal artery of colon. arterial arches of ileum arches formed in the mesentery by branches of the superior mesenteric artery from which vessels (vasa recta, under vas) arise to supply the wall of the ileum. SEE ALSO: intestinal arterial arcades, under arcade. arterial arches of jejunum arches formed in the mesentery by branches of the superior mesenteric artery from which vessels (vasa recta, under vas) arise to supply the walls of the jejunum. SEE ALSO: intestinal arterial arcades, under arcade. arterial a. of lower eyelid SYN: inferior palpebral (arterial) a.. arterial a. of upper eyelid SYN: superior palpebral (arterial) a.. axillary a. SYN: pectorodorsalis muscle. branchial arches typically, 6 arches in vertebrates; in the lower vertebrates, they bear gills; in the higher vertebrates, they appear transiently and give rise to specialized structures in the head and neck. SYN: pharyngeal arches, visceral arches. carpal arches two anastomotic arterial twigs running transversely across the wrist: the palmar or anterior lies in front of the carpus, being formed by palmar carpal branches of the radial and ulnar arteries; the dorsal or posterior lies on the dorsal surface of the carpus, being formed by the dorsal carpal branches of the radial and ulnar arteries. coracoacromial a. a protective a. formed by the smooth inferior aspect of the acromion and the coracoid process of the scapula with the coracoacromial ligament spanning between them. This osseoligamentous structure overlies the head of the humerus, preventing its upward displacement from the glenoid fossa. Corti a. the a. formed by the junction of the heads of Corti inner and outer pillar cells. cortical arches of kidney the portions of renal substance (cortex) intervening between the bases of the pyramids and the capsule of the kidney. costal a. costal margin. a. of cricoid cartilage [TA] the narrow part of the cartilage that encircles the air passage anterior to the lamina. SYN: arcus cartilaginis cricoideae [TA] . crural a. SYN: inguinal ligament. deep crural a. SYN: iliopubic tract. deep palmar (arterial) a. [TA] the arterial a. located deep to the long flexor tendons in the hand. It is formed by the terminal part of the radial artery in conjunction with the deep palmar branch of the ulnar artery. The a. gives rise to palmar metacarpal and princeps pollicis arteries. SYN: arcus palmaris profundus, arcus volaris profundus. deep palmar venous a. [TA] the venous a. that accompanies the deep palmar arterial a.; it usually consists of paired venae comitantes. SYN: arcus venosus palmaris profundus [TA] . dental a. the curved composite structure of the natural dentition and the residual ridge, or the remains thereof after the loss of some or all of the natural teeth. dorsal carpal arterial a. [TA] a vascular network over the dorsal surface of the carpal joints, formed by anastomoses of branches of the anterior and posterior interosseous, and dorsal carpal branches of the radial and ulnar arteries. SYN: rete carpale dorsale [TA] , dorsal carpal network, rete carpi posterius. dorsal venous a. of foot [TA] the a. in the subcutaneous tissue of the dorsum of the foot formed by the dorsal and digital veins; it unites medially with the dorsal vein of the great toe to form the great saphenous vein, and laterally with the dorsal vein of the little toe to form the small saphenous. SYN: arcus venosus dorsalis pedis [TA] . double aortic a. congenital malformation of the aorta that splits and has a right and a left a. instead of a single a.. expansion a. an orthodontic appliance that moves the dental structures distally, bucally, or labially, creating increased molar to molar width and a. length. fallen arches a breaking down of the arches of the foot, either longitudinal, transverse, or both; the resulting deformity is flat (longitudinal) or splay (transverse) foot, or both. fallopian a. SYN: inguinal ligament. femoral a. SYN: inguinal ligament. arches of the foot longitudinal a. of foot, plantar a.. glossopalatine a. SYN: palatoglossal a.. Gothic a. SYN: needle point tracing. Haller arches See lateral arcuate ligament, medial arcuate ligament. hemal arches 1. the arches that collectively comprise the thoracic cage, each consisting of a vertebra (body, pedicle, and transverse processes), the corresponding pair of ribs and their articular cartilages, and the portion of the sternum to which they attach. 2. three or four V-shaped bones located ventral to the bodies of the third to sixth coccygeal vertebrae; they represent intercentra and usually enclose the ventral caudal artery and vein. hyoid a. the second visceral, or branchial, a; the second postoral a. in the branchial a. series. iliopectineal a. [TA] a thickened band of fused iliac and psoas fascia passing from the posterior aspect of the inguinal ligament anteriorly across the front of the femoral nerve to attach to the iliopectineal eminence of the hip bone posteriorly. The iliopectinal a. thus forms a septum which subdivides the space deep to the inguinal ligament into a lateral muscular lacunae and a medial vascular lacunae. When a psoas minor muscle is present, its tendon of insertion blends with the iliopectineal a.. SYN: arcus iliopectineus [TA] , iliopectineal ligament, ligamentum iliopectineale. inferior dental a. SYN: mandibular dental arcade. SYN: arcus dentalis mandibularis [TA] . inferior palpebral (arterial) a. [TA] formed by the medial palpebral artery, which communicates with a branch of the lacrimal artery along the tarsal margin. SYN: arcus palpebralis inferior [TA] , arterial a. of lower eyelid. jugular venous a. [TA] a connecting vein between the two anterior jugular veins in the suprasternal space. SYN: arcus venosus juguli [TA] . labial a. an orthodontic a. wire that approximates the labial surfaces of the teeth. Langer a. SYN: pectorodorsalis muscle. lateral longitudinal a. of foot formed by calcaneus, cuboid, and two lateral metatarsals; the combined a. is supported normally by ligaments, intrinsic muscles, and the tendons of extrinsic muscles of the foot. SYN: arcus pedis longitudinalis pars lateralis. lateral lumbocostal a. SYN: lateral arcuate ligament. lingual a. an orthodontic a. wire that approximates the lingual surfaces of the teeth. longitudinal a. of foot See medial longitudinal a. of foot, lateral longitudinal a. of foot. SYN: arcus pedis longitudinalis. malar a. SYN: zygomatic a.. mandibular a. the first postoral a. in the branchial a. series. SYN: mandibular process. medial longitudinal a. of foot formed by the calcaneus, talus, navicular, three cuneiform bones, and the three medial metatarsals. SYN: arcus pedis longitudinalis pars medialis. medial lumbocostal a. SYN: medial arcuate ligament. nasal a. bridge of the nose, the upward arching roof of the piriform aperture formed by the nasal processes of the maxilla of each side and the nasal bones between them. Eyeglasses rest centrally on various portions of this a.. nasal venous a. an a. formed at the root of the nose by the two supratrochlear veins connected by a transverse vein. neural a. of vertebra SYN: vertebral a.. a. of the palate the vaulted roof of the mouth. palatoglossal a. [TA] one of a pair of ridges or folds of mucous membrane passing from the soft palate to the side of the tongue; it encloses the palatoglossus muscle and forms the anterior margin of the tonsillar fossa. Also demarcates the oral cavity from the isthmus of fauces. SYN: arcus palatoglossus [TA] , anterior pillar of fauces&star, plica anterior faucium&star, anterior palatine a., arcus glossopalatinus, glossopalatine a., glossopalatine fold. palatopharyngeal a. [TA] one of a pair of ridges or folds of mucous membrane that pass downward from the posterior margin of the soft palate to the lateral wall of the pharynx. It encloses the palatopharyngeus muscle and forms the posterior margin of the tonsillar fossa. It also demarcates the isthmus of fauces from the oropharynx. SYN: arcus palatopharyngeus [TA] , plica posterior faucium&star, posterior pillar of fauces&star, pharyngopalatine a., posterior palatine a.. pharyngeal arches SYN: branchial arches. pharyngopalatine a. SYN: palatopharyngeal a.. plantar a. SYN: deep plantar (arterial) a.. plantar arterial a. SYN: deep plantar (arterial) a.. plantar venous a. [TA] the a. formed by the plantar digital veins from the toes, which accompanies the plantar arterial a.. SYN: arcus venosus plantaris [TA] . popliteal a. SYN: arcuate popliteal ligament. posterior a. of atlas [TA] the posterior a. of the atlas that connects the lateral masses of the atlas posteriorly, forming the posterior wall of the vertebral canal at this level. SYN: arcus posterior atlantis [TA] . posterior palatine a. SYN: palatopharyngeal a.. postoral arches the series of branchial arches caudal to the mouth; the first is the mandibular, the second is the hyoid; caudal to the hyoid, the arches are unnamed, and designated only by their postoral number. primitive costal arches arches formed in the thoracic region of the vertebral column in the embryo from the costal processes or costal elements which give rise to the ribs. pubic a. [TA] the a. formed by the symphysis, bodies, and inferior rami of the pubic bones. SEE ALSO: subpubic angle. SYN: arcus pubis [TA] . ribbon a. a thin, ribbon-shaped, rectangular orthodontic a. wire applied to the dental arches so that its widest dimension is parallel to the labial or buccal surfaces of the teeth. subcostal a. infrasternal angle. superciliary a. [TA] a fullness extending laterally from the glabella on either side, above the orbital margin of the frontal bone. SYN: arcus superciliaris [TA] , superciliary ridge. superficial palmar (arterial) a. [TA] the arterial a. in the hand located superficial to the long flexor tendons approximately at the level of a line extrapolated across the palm from the distal side of the outstretched thumb. It is formed principally by the termination of the superficial ulnar artery and is usually completed by a communication with the superficial palmar branch of the radial artery. The a. gives rise to the common palmar digital arteries. SYN: arcus palmaris superficialis [TA] , arcus volaris superficialis. superficial palmar venous a. [TA] the venous a. accompanying the superficial palmar arterial a.; it consists usually of paired venae comitantes and is drained by the superficial ulnar and radial veins. SYN: arcus venosus palmaris superficialis [TA] . superior dental a. SYN: maxillary dental arcade. superior palpebral (arterial) a. [TA] formed by communicating branches of the medial and lateral palpebral arteries. Often two arches are present, one located near the free border of the tarsal plate, the other along the upper border of the tarsus. SYN: arcus palpebralis superior [TA] , arterial a. of upper eyelid. supraorbital a. SYN: supraorbital margin. tarsal a. inferior palpebral (arterial) a., superior palpebral (arterial) a.. tendinous a. [TA] 1. a white, fibrous band attached to bone and/or muscle, arching over and thus protecting neurovascular elements passing beneath it from injurious compression; 2. a linear thickening of the deep fascia of a muscle which provides attachment for ligaments and/or muscle fibers. SYN: arcus tendineus [TA] . tendinous a. of levator ani muscle [TA] a thickened portion of the obturator fascia that extends in an arching line from the pubis posteriorly to the ischial spine and gives origin to part of the levator ani muscle. SYN: arcus tendineus musculi levatoris ani [TA] , arcus tendineus of obturator fascia, arcus tendineus of pelvic diaphragm. tendinous a. of pelvic fascia [TA] a linear thickening of the superior fascia of the pelvic diaphragm extending posteriorly from the body of the pubis alongside the bladder (and vagina in the female) and giving attachment to the supporting ligaments of the pelvic viscera. SYN: arcus tendineus fasciae pelvis [TA] . tendinous a. of soleus muscle [TA] a tendinous a. stretching over—and defining the termination of—the popliteal vessels between the tibia and fibula, which gives origin to the central portion of the soleus muscle. SYN: arcus tendineus musculi solei [TA] . a. of thoracic duct [TA] terminal portion of thoracic duct that turns abruptly to the left, usually at the C7 vertebral level, to enter the superolateral aspect of the junction of the left subclavian and internal jugular veins. SEE ALSO: thoracic duct. SYN: arcus ductus thoracici [TA] . transverse a. of foot the a. formed by the proximal parts of the metatarsal bones, the three cuneiform bones, and the cuboid. SYN: arcus pedis transversalis. Treitz a. SYN: paraduodenal fold. vertebral a. [TA] the posterior projection from the body of a vertebra that encloses the vertebral foramen; it consists of paired pedicles and laminae; the spinous, transverse, and articular processes arise from the a.. In aggregate, the venous arches—and the ligamenta flava that unite them—form the posterior wall of the vertebral (spinal) canal. SYN: arcus vertebrae [TA] , neural a. of vertebra. visceral arches SYN: branchial arches. W-a. a fixed maxillary expansion device attached to the lingual part of the molars, with either bilateral or unilateral extension arms. wire a. a wire conforming to the dental a.; used to restore the normal curve to the denture. zygomatic a. [TA] the a. formed by the temporal process of the zygomatic bone that joins the zygomatic process of the temporal bone. SYN: arcus zygomaticus [TA] , cheek bone (2) , malar a., zygoma (2) .

arch-, arche-, archi-
Combining forms meaning primitive or ancestral; also first, chief, extreme. [G. arche, origin, beginning, + -o-]

archaeocerebellum (ar′ke-o-ser′e-bel′lum)
SYN: archicerebellum. [G. archaios, ancient, + cerebellum]

archaeus (ar-ke′us)
Term first used by Valentine and later by Paracelsus and van Helmont to denote a spirit that presided over and governed bodily processes. SYN: archeus. [L. fr. G. archaios, chief, leader]

archaic (ar-ka′ik)
Ancient; old; in jungian psychology, denoting the ancestral past of mental processes. [G. archaikos, ancient]

LaSalle, U.S. neurologist, 1879–1940. See Meyer-A. loop.

See arch-.

archenteron (ark-en′ter-on)
SYN: primitive gut. [G. arche, beginning, + enteron, intestine]

archeocerebellum (ar-ke-o-ser′-e-bel′ lum)
SYN: vestibulocerebellum.

archeokinetic (ar-ke-o-ki-net′ik)
Denoting a low and primitive type of motor nerve mechanism, such as is found in the peripheral and the ganglionic nervous systems. Cf.:neokinetic, paleokinetic. [G. archaios, ancient, + kinetikos, relating to movement]

archetype (ar′ke-tip)
1. A primitive structural plan from which various modifications have evolved. 2. In jungian psychology, structural manifestation of the collective unconscious. SYN: imago (2) . [G. archetypos, pattern, model, fr. arche, beginning, + typto, to stamp out]

archeus (ar-ke′us)
SYN: archaeus.

See arch-.

archicerebellum (ar′ki-ser-e-bel′um) [TA]
The small, phylogenetically oldest portion of the cerebellum, sometimes called vestibulocerebellum because its afferents arise primarily from the vestibular ganglion and nuclei; in mammals, it is represented by four subdivisions of the cerebellum: nodulus, uvula vermis, flocculus, and lingula of cerebellum. SYN: archaeocerebellum. [archi- + L. cerebellum]

archicortex (ar′ki-kor′teks) [TA]
1. Typically, the phylogenetically older parts of the cerebral cortex. 2. More specifically, the cortex forming the hippocampus. SEE ALSO: allocortex, cerebral cortex. SYN: archipallium. [archi- + L. cortex]

archil (ar′kil) [old C.I. 1242]
A violet dye from the lichens Rocella tinctoria and R. fuciformis. SYN: orchella, orchil, roccellin.


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