| RVA | re-entrant ventricular arrhythmia; right ventricle activation; right vertebral artery |
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| PNET | Primitive Neuro-Ectodermal(-Epithelial) Tumor |
| HbP | primitive hemoglobin |
| PNET | peripheral neuroepithelioma; primitive neuroectodermal tumor |
| RA | radioactive; ragocyte; ragweed antigen; rapidly adapting [receptors]; reactive arthritis; reciprocal... |
| primitive node | A local thickening of the blastoderm at the cephalic end of the primitive streak of the embryo. Synonym: Hensen's knot, Hensen's node, Hubrecht's protochordal knot, primitive knot, protochordal knot. (05 Mar 2000) |
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| primitive palate | In the early embryo, the mesoderm-filled shelf, formed from the medial nasal process, that anteriorly separates the oral cavity below from the primitive nasal cavities above. Synonym: primitive palate. (05 Mar 2000) |
| primitive perivisceral cavity | The space between the ectoderm and endoderm in the gastrula. Synonym: primitive perivisceral cavity. (05 Mar 2000) |
| primitive pit | The depression in the primitive node that serves to connect the notochordal canal with the surface ectoderm and the yolk sac. These connections are referred to as the neurenteric canal. (05 Mar 2000) |
| primitive reticular cell | A cell with processes making contact with those of other similar cell's to form a cellular network; along with the network of reticular fibres, the reticular cell's form the stroma of bone marrow and lymphatic tissues. (05 Mar 2000) |
| primitive ridge | One of the paired ridge's on either side of the primitive groove. (05 Mar 2000) |
| primitive streak | An ectodermal ridge in the midline at the caudal end of the embryonic disk from which arises the intraembryonic mesoderm; achieved by inward and then lateral migration of cells; in human embryos, it appears on day 15 and gives a cephalocaudal axis to the developing embryo. Synonym: germinal streak. (05 Mar 2000) |
| neuroectodermal tumour, primitive | A malignant brain tumour sharing common features and biologic properties with medulloblastoma. Some pathologists and clinicians use the terms interchangeably: they both can disseminate throughout the nervous system and, in some cases, systemically. most lesions arise from the posterior fossa in children under five years of age. The tumour often produces hydrocephalus and symptoms of increased intracranial pressure. Papilledema is often present. (12 Dec 1998) |
| Arantius' ventricle | Inferior part of the rhomboid fossa; the narrow lower end of the fourth ventricle between the two clavae. Synonym: Arantius' ventricle. Origin: L. Writing pen (05 Mar 2000) |
| bulb of lateral ventricle | A rounded elevation in the dorsal part of the medial wall of the posterior horn of the lateral ventricle, produced by the major forceps. (05 Mar 2000) |
| bulb of posterior horn of lateral ventricle of brain | Bulb of posterior horn of lateral ventricle of the brain; a curved elevation on the inner wall of the posterior horn produced by the fibres of the forceps major of the corpus callosum as they bend backward into the occipital lobe. Synonym: bulb of posterior horn of lateral ventricle of brain. (05 Mar 2000) |
| vein of lateral recess of fourth ventricle | A small vein originating in the cerebellar tonsil, coursing by the lateral recess of the fourth ventricle on its way to terminate in the petrosal vein. Synonym: vein of lateral recess of fourth ventricle. (05 Mar 2000) |
| ventricle | <anatomy> The paired (right and left) more muscular chambers of the heart that pump blood into the pulmonary (right ventricle) and systemic (left ventricle) circulation. (27 Sep 1997) |
| ventricle of cerebral hemisphere | A cavity shaped somewhat like a horseshoe in conformity with the general shape of the hemisphere; each lateral ventricle communicates with the third ventricle through the interventricular foramen of Monro, and expands from there forward into the frontal lobe as the anterior horn as well as caudally over the thalamus as the central part or cella media which, behind the thalamus, curves ventrally and laterally, then forward into the temporal lobe as the inferior horn; from the apex of the curve a variably sized posterior horn extends back into the white matter of the occipital lobe. The large choroid plexus of the lateral ventricle invades the cella media and the inferior horn (but not the anterior and posterior horn) from the medial side. Synonym: ventriculus lateralis, ventricle of cerebral hemisphere. (05 Mar 2000) |
| ventricle of diencephalon | A narrow, vertically oriented, irregularly quadrilateral cavity in the midplane, extending from the lamina terminalis to the rostral opening of the mesencephalic aqueduct. This ventricle communicates at its rostrodorsal corner with each of the two lateral ventricles through the left and right interventricular foramen of Monro. Its narrow roof is formed by the tela choroidea which is attached on either side to the tenia thalami; its lateral wall by the medial surface of the thalamus and, below the hypothalamic sulcus, by the hypothalamus which also forms its floor. In lateral profile, the third ventricle exhibits a number of recesses: in its floor, from before backward, 1) the preoptic recess in the acute angle between the base of the lamina terminalis and the dorsum of the optic chiasm, 2) the infundibular recess extending ventrally into the infundibulum but (in humans) not into the hypophysial stalk, and 3) the mamillary or inframamillary recess caused by the protrusion of the mamillary bodies into the ventricle. From its dorsocaudal corner, the pineal recess extends caudally into the pineal stalk. Synonym: ventriculus tertius, diacele, ventricle of diencephalon. (05 Mar 2000) |