Large natural streams of FRESH WATER formed by converging tributaries and which empty into a body of water (lake or ocean).

Interstitial space between cells, occupied by INTERSTITIAL FLUID as well as amorphous and fibrous substances. For organisms with a CELL WALL, the extracellular space includes everything outside of the CELL MEMBRANE including the PERIPLASM and the cell wall.

Space between the dura mater and the walls of the vertebral canal.

Invisible boundaries surrounding the individual's body which are maintained in relation to others.

The awareness of the spatial properties of objects; includes physical space.