Bird vertebrae are (a) acoelous (b) heterocoelous (c) amphicoelous (d) procoelous.
Option B Bird vertebrae are heterocoelous i.e., the centra of vertebrae have saddle shaped ends. Acoelous refers to vertebrae that are flat on both ends (mammals). Amphicoelous means both ends of the centrum are concave (fish). Procoelous means concave in front and convex in back (anurans and reptiles).
