| septum pellucidum | 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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| septum penis | The portion of the tunica albuginea incompletely separating the two corpora cavernosa of the penis. (05 Mar 2000) |
| septum primum | A crescentic septum in the embryonic heart that develops on the dorsocephalic wall of the originally single atrium and initiates its partitioning into right and left chambers; the tips of the septum grow toward and fuse with the atrioventricular canal cushions. (05 Mar 2000) |
| septum rectovaginale | The fascial layer between the vagina and the lower part of the rectum. Synonym: septum rectovaginale. (05 Mar 2000) |
| septum rectovesicale | A fascial layer that extends superiorly from the central tendon of the perineum to the peritoneum between the prostate and rectum. Synonym: septum rectovesicale, Denonvilliers' aponeurosis, rectovesical fascia, Tyrrell's fascia. (05 Mar 2000) |
| septum scroti | An incomplete wall of connective tissue and nonstriated muscle (dartos fascia) dividing the scrotum into two sacs, each containing a testis. Synonym: septum scroti. (05 Mar 2000) |
| septum secundum | The second of two major septal structures involved in the partitioning of the atrium, developing later than the septum primum and located to the right of it; like the septum primum, it is crescentic, but its tips are directed toward the sinus venosus, and it is more heavily muscular; it remains an incomplete partition until after birth, with its unclosed area constituting the foramen ovale. (05 Mar 2000) |
| septum sinuum frontalium | The bony partition between the right and left frontal sinuses; it is often deflected to one side of the middle line. Synonym: septum sinuum frontalium. (05 Mar 2000) |
| septum sinuum sphenoidalium | The bony partition between the two sphenoidal sinuses, often deflected to one side of the mid line. Synonym: septum sinuum sphenoidalium. (05 Mar 2000) |
| septum spurium | A septum in the right atrium of the embryonic heart formed by the right venous valve and its continuation onto the dorsocephalic wall of the atrium; in human embryos, it reaches its fullest development during the third month and then undergoes regression, taking no part in atrial partitioning (hence its designation as false); reduced portions persist as the valve of the inferior vena cava and the valve of the coronary sinus. (05 Mar 2000) |
| septum tubae | A very thin horizontal plate of bone forming two saemicanals, the upper, smaller, for the tensor tympani muscle, the lower, larger for the auditory tube; its termination in the middle ear is the processus cochleariformis. Synonym: septum canalis musculotubarii, septum of musculotubal canal, septum tubae. (05 Mar 2000) |
| septum, ventricular | The wall between the two lower chambers (the right and left ventricles) of the heart. (12 Dec 1998) |
| sinus septum | A small fold forming the medial end of the valve of the inferior vena cava; it is developed from the dorsal wall of the embryonic sinus venosus. (05 Mar 2000) |
| spiral bulbar septum | See: spiral septum. (05 Mar 2000) |
| spiral septum | A septum dividing the embryonic bulbus cordis into pulmonary and aortic outflow tracts from the developing heart; the distal spiral septum is derived from the right and left endocardial cushions and so separates the pulmonary and aortic orifices; the proximal spiral septum is the portion of the septum that is incorporated into the membranous part of the interventricular septum. (05 Mar 2000) |