Phys. [a. L. bivium a place where two ways meet; see prec.] The two hinder ambulacra of Echinoderms.
1877. Huxley, Anat. Inv. Anim., ix. 570. It is possible in any of the Echinidea, to separate the three anterior ambulacra, as the trivium, from the two posterior, the bivium; and in the fossil genus Dysaster, this separation of the ambulacra into trivium and bivium exists naturally.
