| sinus of the vena cava | The portion of the cavity of the right atrium of the heart that receives the blood from the venae cavae; it is separated from the rest of the atrium by the crista terminalis. Synonym: sinus venarum cavarum. (05 Mar 2000) |
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| sinus of valsalva | The dilatation of the aortic wall behind each of the cusps of the aortic valve. (12 Dec 1998) |
| sinus paranasales | Air-filled extensions of the respiratory part of the nasal cavity into the frontal, ethmoid, sphenoid, and maxillary cranial bones. They vary in size and form in different individuals and are lined by the ciliated mucous membranes of the nasal cavity. (12 Dec 1998) |
| sinus pause | A spontaneous interruption in the regular sinus rhythm, the pause lasting for a period that is not an exact multiple of the sinus cycle. See: sinus arrest, sinus standstill. (05 Mar 2000) |
| sinus petrosus inferior | A paired dural venous sinus running in the groove on the petrooccipital fissure connecting the cavernous sinus with the superior bulb of the internal jugular vein. Synonym: sinus petrosus inferior, Englisch's sinus. (05 Mar 2000) |
| sinus petrosus superior | A paired dural venous sinus in the groove along the crest of the petrous temporal bone, connecting the cavernous sinus with the termination of the transverse sinus or beginning of the sigmoid sinus. Synonym: sinus petrosus superior. (05 Mar 2000) |
| sinus phlebitis | Inflammation of a cerebral sinus. (05 Mar 2000) |
| sinus pocularis | A minute pouch in the prostate opening on the summit of the seminal colliculus, the analogue of the uterus and vagina in the female, being the remains of the fused caudal ends of the paramesonephric ducts. Synonym: utriculus prostaticus, masculine uterus, Morgagni's sinus, sinus pocularis, uterus masculinus, vagina masculina, vesica prostatica, Weber's organ. (05 Mar 2000) |
| sinus posterior | A deep groove above the pyramidal eminence extending to the incudal fossa in the posterior wall of the tympanic cavity. (05 Mar 2000) |
| sinus prostaticus | The groove on either side of the urethral crest in the prostatic part of the urethra into which the prostatic ducts open. Synonym: sinus prostaticus. (05 Mar 2000) |
| sinus rectus | straight sinus |
| sinus reflex | See: carotid sinus syndrome. (05 Mar 2000) |
| sinus renalis | The cavity of the kidney, containing the calyces and pelvis of the ureter and the segmental vesels embedded within a fatty matrix. The renal sinuses cause the kidneys to appear hollow or C-shaped on cross section or medical imaging. Synonym: sinus renalis. (05 Mar 2000) |
| sinus reuniens | An obsolete term for sinus venosus. Rhomboidal sinus Sinus rhomboidalis, a dilation of the central canal of the spinal cord in the lumbar region. Synonym: rhombocele. (05 Mar 2000) |
| sinus rhythm | The normal regular cardiac rhythm stimulated by the sinoatrial node. (27 Sep 1997) |