septum

n., pl., -ta (-tə).
A thin partition or membrane that divides two cavities or soft masses of tissue in an organism: the nasal septum; the atrial septum of the heart.

[New Latin sēptum, from Latin saeptum, partition, from neuter past participle of saepīre, to enclose, from saepēs, fence.]

(SEP-tuhm)

noun, plural septa (SEP-tuh)
A dividing wall, in an animal or a plant. For example, the partition between the nostrils.

Etymology
Latin saeptum, partition, from neuter of saeptus, past participle of saepire, to enclose, from saepes, fence.

Usage
"A 10-year-old Massachusetts girl wound up in hospital after trying to achieve the pierced nose look with a magnetic earring on her nostril... The magnets were so powerful that they had broken from the rings and become embedded on either side of the nasal septum, out of reach of available medical instruments." — U.S. Girl Gets Painful Lesson in Attraction, Reuters, May 13, 1998.

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1. A low wall or balustrade which divided the nave of the ancient basilican church into a middle section (for the clergy) and two side sections (for the laity).
2. A low wall around a tomb.
3. The enclosure of the Holy Table made by the altar rails in a church.

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Pl. septa [L.] a wall or partition dividing a body space or cavity.
Some septa are membranous, some are composed of bone, and some of cartilage. The wall separating the atria of the heart, for instance, is called the interatrial septum.

• atrioventricular s. — the part of the membranous portion of the interventricular septum between the left ventricle and the right atrium.
• bulbar s. — a septum, formed by merging of the bulbar cushions, divides the bulbus cordis into aortic and pulmonary outflows.
• cystic s. pellucidum — an embryonic malformation resulting in the formation of a fluid-filled cavity in the septum between the two lateral ventricles, instead of the normal glial raphe.
• horizontal s. — in the avian body cavity there is no diaphragm but the cavity is divided into three compartments; this is one of the divider organs; thin and membranous for the most part, the septum forms the ventral boundary of paired cavities containing the lungs.
• interalveolar s. — the bony partition between adjacent tooth sockets.
• interatrial s. — the partition separating the right and left atria of the heart.
• interlobar s. — a septum that converts an organ into lobes.
• intermuscular s. — fascial septum separating muscle masses.
• interorbital s. — bony partition between the large orbital cavities of birds.
• interventricular s. — the partition separating the right and left ventricles of the heart. See also ventricular septum.
• s. lucidum — septum pellucidum (below).
• median s. — membranous partition in the ventral median fissure of the spinal cord.
• oblique s. — a partition which divides the lower part of the bird's body cavity; the part of the cavity cranial to this septum contains the thoracic air sacs and the thoracic parts of the cervical and clavicular air sacs. The part of the body cavity caudal to this septum contains heart, liver, spleen, gastrointestinal, urinary and reproductive tracts and abdominal air sacs.
• orbital s. — a fold which detaches from the periorbital fascia at the orbital rim, and which leads into the tarsi, the thickened margins of the eyelids.
• s. pellucidum, pellucid s. — the triangular double membrane separating the anterior horns of the lateral ventricles of the brain. Called also septum lucidum, telencephalic septum.
• pharyngeal s. — a transitory partition between the mouth and pharynx in the embryo.
• s. primum — a septum in the embryonic heart, dividing the primitive atrium into right and left chambers.
• rectovaginal s. — the membranous partition between the rectum and vagina.
• rectovesical s. — a membranous partition separating the rectum from the prostate and urinary bladder.
• s. secundum — develops during embryonic life to contribute to the formation of the foramen ovale between the cardiac atria.
• telencephalic s. — see septum pellucidum (above).
• s. transversum — a major contributor to the development of the diaphragm and the liver.
• truncal s. — a partition which develops from truncal cushions within the truncus arteriosus and contributes to the separation of cardiac outflow into pulmonary and systemic circulations.
• urorectal s. — a septum which divides the urinary passages from the hindgut in the embryo by horizontally partitioning the cloaca.