Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
A septum (Latin: something that encloses; plural Septa) is a partition separating two cavities or spaces. Septum or septa may refer to:
- Septum, a partition of two cavities or spaces
- Septum (marine biology), in marine biology, a thin membrane separating each shell chamber in cephalopods that retained their external shell (Cephalopod Septa]]: walls between each chamber, or siphuncle, in shells of nautiloids, ammonites, and belemnites; i.e. cephalopods that retain an external shell.)
- The wall dividing the right side of the heart from the left side.
- Septum nasi or septum, the cartilage wall separating the nostrils (Nasal septum: the cartilage wall separating the nostrils of the human nose. Often deviated or perforated through physical injury or cocaine abuse.)
- Septum pellucidum or septum lucidum, a thin structure separating two fluid pockets in the brain
- Interatrial septum, the wall of tissue that separates the left and right atria of the heart
- Interventricular septum or median septum, the wall separating the left and right ventricles of the heart
- Lingual septum, a vertical layer of fibrous tissue that separates the halves of the tongue
- Orbital septum, a palpabral ligament in the upper and lower eyelids
- Uterine septum or uterus didelphys, a malformation of the uterus
- Septum, in mycology, the wall partitioning fungal hyphae into discrete cells
- Septation, microbiology, the process whereby a cell divides into two cells
- Fungi produce septa to partition filamentous hyphae into discrete cells.
Histological septa are seen throughout most tissues of the body, particularly where they are needed to stiffen a soft cellular tissue, and they also provide planes of ingress for small blood vessels. Because the dense collagen fibres of a septum usually extend out into the softer adjacent tissues, microscopic fibrous septa are less clearly defined than the macroscopic types of septa listed above. In rare instances, a septum is a cross-wall.
The septum is also found within the chambers of the heart. It provides strength to the walls of the heart and separates the left and right sides of the heart.
In chemistry and other experimental sciences, septa are rubber stoppers which seal flasks or bottles. They are designed to be pierced by a needle or cannula which allows fluids to be transferred. Septa are often used together with Schlenk flasks and Schlenk lines to handle oxygen- or moisture-sensitive materials.
Septum magneta and electrostatic septum are two types of septa that can deflect an ejected beam while not affecting the orbiting beam. These devices are used with a circular particle beam accelerator to inject or eject a beam of particles to or from an accelerator.
Part of the limbic system that regulates emotions and the ability to learn and control impulses as well as such drives as sex, hunger, thirst, aggression, and fear. The septum (or septal nuclei) in the brain is named for its approximate shape (partition). The septum is rich with nicotonic cholinergic receptors.
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