A phagocytic sleeve that is part of a sheathed arteriole of the spleen, and is sometimes referred to as a splenic ellipsoid. It is a spindle-shaped thickening in the walls of the second part of the arterial branches forming the penicilli in the spleen [ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3204613 http://en.wikipedia.org/wiki/Schweigger-Seidel_sheath ]