| transparent septum | A thin plate of brain tissue, containing nerve cells and numerous nerve fibres, that is stretched like a flat, vertical sheet between the column and body of fornix below, the corpus callosum above and anteriorly; it is usually fused in the median plane with its partner on the opposite side so as to form a thin, median partition between the left and right frontal horn of the lateral ventricles; in less than 10% of humans there is a blind, slitlike, fluid-filled space between the two transparent septa, the cavity of septum pellucidum. The transparent septum is continuous ventralward through the interval between the corpus callosum and the anterior commissure with the precommissural septum and subcallosal gyrus. See: cavity of septum pellucidum, septal area. Synonym: septum pellucidum, septum lucidum. (05 Mar 2000) |
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| endovenous septum | Septum endovenosum, a remnant of the primitive separation between veins which fused to form a definitive trunk, such as the trunk leading to the left common iliac and the left renal veins. (05 Mar 2000) |
| transverse septum | The mesodermal mass separating the pericardial and peritoneal cavities; it is covered with mesothelium except where intimately associated with the liver which originally develops within it; the septum is definitively incorporated into the diaphragm as the central tendon. (05 Mar 2000) |
| femoral septum | The delicate fibrous membrane that closes the femoral ring at the base of the femoral canal. Synonym: septum femorale, Cloquet's septum, crural septum. (05 Mar 2000) |
| urogenital septum | The coronally placed ridge formed by the caudal portion of the urogenital ridges fusing in the midline of the embryo; it lies between the hindgut dorsally and the bladder ventrally. (05 Mar 2000) |
| urorectal septum | In embryos, a partition dividing the cloaca into a dorsal, rectal portion and a ventral portion called the urogenital sinus; reaching the cloacal membrane at about the time of its disintegration, the urorectal septum divides the cloacal exit into an anal and a urogenital orifice. Synonym: urorectal fold. (05 Mar 2000) |
| lamina of septum pellucidum | One of the two thin layers of the transparent septum, which extend from the corpus callosum to the fornix; often separated from each other by a space, the cavity of septum pellucidum. Synonym: lamina septi pellucidi. (05 Mar 2000) |
| lingual septum | The median vertical fibrous partition of the tongue merging posteriorly into the aponeurosis of the tongue. Synonym: septum linguae, septum of tongue. (05 Mar 2000) |
| abducens nucleus | Nucleus of abducent nervenucleus abducentis, a group of motor neurons in the lower part of the pons, innervating the lateral rectus muscle of the eye; unique among motor cranial nerve nuclei in that it consists of two distinct populations of neurons: neurons that give rise to fibres forming the abducens nerve root and those internuclear neurons whose processes cross the midline, ascend in the opposite medial longitudinal fasciculus, and terminate upon specific oculomotor neurons; considered a primary centre for mechanisms controlling conjugate horizontal gaze. Synonym: nucleus nervi abducentis. (05 Mar 2000) |
| accessory cuneate nucleus | A cell group lateral to the cuneate nucleus which receives posterior-root fibres corresponding to the proprioceptive innervation of the arm and hand; it projects to the cerebellum by way of the cuneocerebellar tract, and can be considered the upper-extremity equivalent of the thoracic nucleus. Synonym: nucleus cuneatus accessorius, external cuneate nucleus, lateral cuneate nucleus, Monakow's nucleus. (05 Mar 2000) |
| almond nucleus | Almond-shaped group of basal nuclei anterior to the inferior horn of the lateral ventricle of the brain, within the temporal lobe. The amygdala is part of the limbic system. (12 Dec 1998) |
| ambiguous nucleus | A very slender, longitudinal column of motor neurons in the ventrolateral medulla oblongata; its efferent fibres leave with the vagus and glossopharyngeal nerve and innervate the striated muscle fibres of the pharynx (including the musculus levator veli palatini) and the vocal cord muscles of the larynx. Synonym: ambiguous nucleus. (05 Mar 2000) |
| amygdaloid nucleus | Almond-shaped group of basal nuclei anterior to the inferior horn of the lateral ventricle of the brain, within the temporal lobe. The amygdala is part of the limbic system. (12 Dec 1998) |
| anterior extremity of caudate nucleus | The head or anterior extremity of the caudate nucleus projecting into the anterior horn of the lateral ventricle. Synonym: caput nuclei caudati, anterior extremity of caudate nucleus. (05 Mar 2000) |
| anterodorsal thalamic nucleus | anterodorsal thalamic nucleus |