The longitudinal system is discontinuous, and is subdivided into proximal, medial and distal portions.
According to Armstrong, anthracene behaves unsymmetrically towards substituents, and hence one lateral ring differs from the other; he represents the molecule as consisting of one centric ring, the remaining medial and lateral ring being ethenoid.
For general purposes, however, the symbol (2), in which the lateral rings are benzenoid and the medial ring fatty, represents quite adequately the syntheses, decompositions, and behaviour of anthracene.
All that can be said at present about this difficult etymology is that in the non-Semitic Babylonian the medial m represented quite evidently an indeterminate nasal which could also be indicated by the combination rig.
The retention of medial f which in Latin became b; 2.