| fourth finger | Fourth finger. Synonym: digitus annularis, fourth finger. (05 Mar 2000) |
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| fourth heart sound | The sound produced in late diastole in association with ventricular filling due to atrial systole and related to reduced ventricular compliance. It is a low frequency oscillation that may be normal at older ages owing to a physiologic decline in ventricular compliance but is nearly always abnormal at younger ages if it is of high intensity or palpable. It is common in ventricular hypertrophy, particularly with hypertension, and is almost invariable during acute myocardial infarction. Fourth heart sounds may arise from the right or left ventricle or both. Synonym: atrial sound. (05 Mar 2000) |
| fourth parallel pelvic plane | The lower opening of the true pelvis, bounded anteriorly by the pubic arch, laterally by the rami of the ischium and the sacrotuberous ligament on either side, and posteriorly by these ligaments and the tip of the coccyx. Synonym: apertura pelvis inferior, apertura pelvis minoris, fourth parallel pelvic plane, pelvic outlet, pelvic plane of outlet, plane of outlet. (05 Mar 2000) |
| fourth stage of labour | The hour or two after delivery when the tone of the uterus is established and the uterus contracts down again. (12 Dec 1998) |
| fourth turbinated bone | A small concha frequently present on the posterosuperior part of the lateral nasal wall; it overlies the supreme nasal meatus. Synonym: concha nasalis suprema, fourth turbinated bone, highest concha, highest turbinated bone, Santorini's concha, concha santorini, supraturbinal, supreme concha, supreme turbinated bone, turbinated body. (05 Mar 2000) |
| fourth ventricle | A cavity of irregular tentlike shape extending from the obex rostralward to its communication with the sylvian aqueduct, enclosed between the cerebellum dorsally and the rhombencephalic tegmentum ventrally, having a rhomboid-shaped floor (rhomboid fossa) and a tentlike roof which in its caudal part is formed by the tela choroidea and the posterior medullary velum, in its middle part by the white matter of the cerebellum, and in its narrowing rostral part (recessus superior) by the anterior medullary velum. The fourth ventricle reaches its greatest width at the pontomedullary transition, where it expands laterally behind the cerebellar peduncles into the spoutlike lateral recess, and its greatest height at the fastigial recess, which reaches up into the cerebellar white matter. Direct communication of the brain's ventricle system and the subarachnoid space is established at the level of the fourth ventricle by a median opening in the tela choroidea, the medial aperture of Magendie's foramen, which opens into the cerebellomedullary cistern, and on both sides by the lateral aperture or foramen of Luschka, which connects the lateral recess with the interpeduncular cistern. Synonym: ventriculus quartus, ventricle of rhombencephalon. (05 Mar 2000) |
| fourth ventricle mass | <radiology> IN ADULTS: choroid plexus papilloma, haemangioblastoma, vermian metastasis, arteriovenous malformation (AVM), inflammatory mass/cyst IN KIDS: medulloblastoma, uniform enhancement, homogeneous, ependymoma, patchy enhancement, heterogeneous, calcified (12 Dec 1998) |
| lateral recess of fourth ventricle | The narrow recess of the ventricle that extends laterally over, and down along the side of, the inferior cerebellar peduncle and the overlying cochlear nuclei; at its tip it opens by way of Luschka's foramen into the interopeduncular cistern of the subarachnoid space. By way of this recess, part of the choroid plexus of the fourth ventricle protrudes into the subarachnoid space. Synonym: recessus lateralis ventriculi quarti. (05 Mar 2000) |
| communicating branches of auriculotemporal nerve to facial nerve | <anatomy, nerve> Branches conveying fibres from the auriculotemporal nerve to the facial nerve. Synonym: rami communicantes nervi auriculotemporalis cum nervo faciali. (05 Mar 2000) |
| communicating branches of lingual nerve to hypoglossal nerve | <anatomy, nerve> Communicating branches between the lingual nerve (from mandibular nerve) and hypoglossal nerve forming a plexus on the hypoglossus muscle. Synonym: rami communicantes nervi lingualis cum nervo hypoglosso. (05 Mar 2000) |
| communicating branch of facial nerve with glossopharyngeal nerve | <anatomy, nerve> A small branch from the digastric branch of the facial nerve to the glossopharyngeal nerve. Synonym: ramus communicans cum nervo glossopharyngeo, Haller's ansa. (05 Mar 2000) |
| communicating branch of glossopharyngeal nerve with auricular branch of vagus nerve | <anatomy, nerve> A small branch of the glossopharyngeal nerve which joins the auricular branch of the vagus, conveying tactile fibres. Synonym: ramus communicans cum nervo glossopharyngeo, ramus communicans nervi glossopharyngei cum ramo auriculari nervi vagalis. (05 Mar 2000) |
| communicating branch of lacrimal nerve with zygomatic nerve | <anatomy, nerve> Nerve branch by which postsynaptic parasympathetic (secretomotor) fibres from the pterygopalatine ganglion are transferred from the zygomatic nerve to the lacrimal nerve (heretofore purely sensory) for distribution to the lacrimal gland. Synonym: ramus communicans nervi lacrimalis cum nervo zygomatico. (05 Mar 2000) |
| communicating branch of median nerve with ulnar nerve | <anatomy, nerve> Branch of median nerve joining the ulnar nerve in the hand; the anterior interosseous branch of the median nerve may also communicate with the ulnar nerve in the proximal forearm. Synonym: ramus communicans nervi mediani cum nervo ulnari. (05 Mar 2000) |
| communicating branch of superior laryngeal nerve with recurrent laryngeal nerve | <anatomy, nerve> Branch of internal branch of superior laryngeal nerve communicating with the recurrent laryngeal nerve in the wall of the laryngopharynx supplying sensory fibres to the latter. Synonym: ramus communicans nervi laryngei recurrentis cum ramo laryngeo interno, ramus communicans nervi laryngei superioris cum nervo laryngeo recurrenti, Galen's anastomosis, Galen's nerve. (05 Mar 2000) |