(L. anterior: that is in front) Away from the stem, midrib, pistil or other organ; e.g. on a lipped flower, the bottom lip is anterior, the top lip is posterior; sometimes the anterior lip is less correctly called inferior or exterior; said of floral organs on the side of the flower farthest from the axis; in transversely inserted leaves, the side or surface oriented away from the axis. Anterior for bivalves: The end of the shell where the head and foot lie; opposite the end where the siphons are located (photo). Often most easily identified by the posterior location of the pallial sinus, or by the fact that the umbo is usually anterior to the hinge ligament. Cf. posterior.