OS, gen, os's is, pi. os'sa

[L. bone.] [BNA] A bone. the occipital bone which unites with, the condylic portions about the fourth or fifth year. the largest of the carpal bones, the inner of the two middle bones of the second row; it articulates with the 2d, 3d, and 4th metacarpal, multangulum minus, hamatum, naviculare, and lunatum. found at the back of the carpus between the scaphoid, OS magnum, and trapezoid; it is developed from an independent cartilage of early fetal life but is usually merged with the scaphoid; it occurs normally in most monkeys. spinal column formed by the fusion of four rudimentary vertebfEe; it articulates with the sacrum. phalanx in the foot of the horse.