| frontal sinus | One of the paired, but seldom symmetrical, air spaces located between the inner and outer compact layers of the frontal bone. (12 Dec 1998) |
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| frontal sinus aperture | One of a pair of openings in the floor of the frontal sinuses in the nasal part of the frontal bone, through which the frontal sinuses communicate with the ethmoidal infundibulum via the frontonasal duct. Synonym: apertura sinus frontalis. (05 Mar 2000) |
| longitudinal sinus | See: inferior sagittal sinus, superior sagittal sinus. Longitudinal vertebral venous sinus, large, plexiform veins forming portions of the anterior internal vertebral venous plexus lying on the posterior surfaces of the vertebral bodies on either side of the posterior longitudinal ligament. Synonym: sinus vertebrales longitudinales. Luschka's sinus, venous sinus in the petrosquamous suture. (05 Mar 2000) |
| lymphatic sinus | The channels in a lymph node crossed by a reticulum of cells and fibres and bounded by littoral cells; there are subcapsular, trabecular, and medullary sinus's. Synonym: lymph sinus. Maier's sinus, an infundibuliform depression on the internal surface of the lacrimal sac which receives the lacrimal canaliculi. Marginal sinuses of placenta, discontinuous venous lakes at the margin of the placenta. (05 Mar 2000) |
| lymph sinus | The channels in a lymph node crossed by a reticulum of cells and fibres and bounded by littoral cells; there are subcapsular, trabecular, and medullary sinus's. Synonym: lymph sinus. Maier's sinus, an infundibuliform depression on the internal surface of the lacrimal sac which receives the lacrimal canaliculi. Marginal sinuses of placenta, discontinuous venous lakes at the margin of the placenta. (05 Mar 2000) |