Rib

Rib (from O. Eng. ribb; the word appears in many Teutonic languages, cf. Ger. Rippe, Swed. reb), in anatomy, the primary meaning, one of the series of elastic arched bones (costae) which form the casing or framework of the thorax (see Skeleton: Axial). The word is in meaning transferred to many objects resembling a rib in shape or function. In architecture, it is thus used of the arches of stone which in medieval work constitute the skeleton of the vault, and carry the shell or web. Although in the Roman vault the rih played an important element in its construction, it was generally hidden in the thickness of the vault and was made subservient to its geometrical surfaces. The Gothic masons, on the other hand, reversed the process, and not only made the vaulting surface subservient to the rib, but by mouldings rendered the latter a highly decorative feature. The principal ribs are the transverse (arc double au), the diagonal (arc ogive)  and the wall rib (f ormeret) . Those of less importance are the intermediate, the ridge and lierne ribs. The ridge-rib is one first introduced into the vault to resist the thrust of the intermediate ribs between the wall and diagonal ribs; it also served to mark the junction of the filling-in or web of vaults in those cases where the courses dipped toward the diagonal rib. (See Vault.) A lierne rib (the term is borrowed from the French) is a short rib, introduced into the vaulting in the Early Perpendicular period, which coupled together the transverse and intermediate ribs; in the later period the "lierne" rib becomes one of the chief features of the "Stella" vault (see further Vault).