| raphe palati | A rather narrow, low elevation in the centre of the hard palate that extends from the incisive papilla posteriorly over the entire length of the mucosa of the hard palate. Synonym: raphe palati, palatine ridge. (05 Mar 2000) |
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| raphe palpebralis lateralis | A narrow fibrous band in the lateral part of the orbicularis oculi muscle formed by the interlacing of fibres passing through the upper and lower eyelids. Synonym: raphe palpebralis lateralis, palpebral raphe. (05 Mar 2000) |
| raphe penis | The continuation of the raphe of the scrotum onto the underside of the penis. Synonym: raphe penis. (05 Mar 2000) |
| raphe perinei | The central anteroposterior line of the perineum, most marked in the male, being continuous with the raphe of the scrotum. Synonym: raphe perinei. (05 Mar 2000) |
| raphe pharyngis | The central line of the pharynx posteriorly where the muscular fibres meet and partly interlace. Synonym: raphe pharyngis. (05 Mar 2000) |
| raphe pontis | The continuation of the raphe medullae oblongatae into the pars dorsalis (or tegmentum) pontis. (05 Mar 2000) |
| raphe pterygomandibularis | A tendinous thickening of the buccopharyngeal fascia, separating and giving origin to the buccinator muscle anteriorly and the superior constrictor of the pharynx posteriorly. Synonym: raphe pterygomandibularis, pterygomandibular ligament. (05 Mar 2000) |
| raphe retinae | The horizontal line separating the superior and inferior portions of the temporal retina over which the retinal nerve fibres do not course. (05 Mar 2000) |
| raphe scroti | A central line, like a cord, running over the scrotum from the anus to the root of the penis; it marks the position of the septum scroti. Synonym: raphe scroti, Vesling's line. (05 Mar 2000) |
| raphespinal fibres | Nerve fibres originating from cells of the nuclei raphe magnus, pallidus, and obscurus of the pons and medulla and terminating in the spinal cord gray matter; fibres involved in the descending inhibition of nociceptive input in the dorsal (posterior) horn; they contain serotonin. (05 Mar 2000) |
| raphides | Needle-like crystals that occur in bundles in the vacuoles of some plant cells. (09 Oct 1997) |
| rapid canities | Whitening of hair overnight or over a few days; in the latter case, may be seen in alopecia areata, when surviving pigmented hairs are preferentially shed from gray hair. (05 Mar 2000) |
| rapid decompression | Sudden severe expansion of gases due to a reduction in ambient pressure. Synonym: explosive decompression. (05 Mar 2000) |
| rapid demineralization | <radiology> Immobilization atrophy, Sudeck's atrophy (reflex sympathetic dystrophy), rheumatoid or psoriatic (rarely in inflammatory states) see also: vanishing bone (spontaneous osteolysis) syndromes (12 Dec 1998) |
| rapid eye movement sleep | REM sleep, that state of deep sleep in which rapid eye movements, alert EEG pattern, and dreaming occur; several central and autonomic functions are distinctive during this state. (05 Mar 2000) |