Pl. costæ. The Latin word for rib, applied in Natural History and Physiology to various rib-like parts, also (after mod.Romanic costa, F. coste, côte side, border) to the edges of certain parts.
a. Anat. A rib. b. Bot. The midrib of a leaf. c. Entom. The ‘rib’ or ‘vein’ nearest to the anterior margin of an insect’s wing; also the anterior margin itself. d. Conchol. A rib-like ridge on a shell, etc.
1866. Treas. Bot., s.v., A leaf may have many costæ.
1866. Tate, Brit. Mollusks, iv. 139. The ribless condition results from the disappearance of the costæ upon the shell.
1870. Bentley, Bot., 145. One large central vein … called the midrib or costa.
1873. Mivart, Elem. Anat., 35. Each rib, or costa,… has a double attachment to the backbone.
1875. W. Houghton, Sk. Brit. Insects, 87. Costa (i.e., front edge of the wings).
1882. Syd. Soc. Lex., Costa … in Entomology, the vein next the anterior margin of the wing.
