noun
: a bony or cartilaginous arch extending ventrally from the spinal column:
a. : the arch formed by a vertebra and an associated pair of ribs
b.
(1) : an arch on the ventral surface of each caudal vertebra of a lower vertebrate (as a fish or reptile) usually considered to consist of the extended and ventrally fused parapophyses of the vertebra
(2) : such an arch together with its dependent hemal spine forming a V-shaped or Y-shaped ventral prolongation of a caudal vertebra — called also chevron bone