. The American journal of roentgenology, radium therapy and nuclear medicine . ence of this ossicle varies with the 406 The Supernumerary Pedal Bones opinions ol the diflerent writers. Someconsider as the trigonum the ossicle ineither its fused or unfused state. Othersinsist on the independent form. In generalit would appear that it can be either foundentirely independent, or distinctly markedoff on the surface in about 10 per cent ofall feet. The os trigonum may be connected withthe astragalus by means of fibrous tissue,or the opposed surfaces of the bones maybe covered with a thin line of hy
. The American journal of roentgenology, radium therapy and nuclear medicine . ence of this ossicle varies with the 406 The Supernumerary Pedal Bones opinions ol the diflerent writers. Someconsider as the trigonum the ossicle ineither its fused or unfused state. Othersinsist on the independent form. In generalit would appear that it can be either foundentirely independent, or distinctly markedoff on the surface in about 10 per cent ofall feet. The os trigonum may be connected withthe astragalus by means of fibrous tissue,or the opposed surfaces of the bones maybe covered with a thin line of hyaline cartil- There is no record in the literature ot thisossicle having been described, other thanthat reported by the writer, and sinceit has never been found at dissection, itmust be classed with those supernumerarystructures which are still considered doubt-ful. Figure 4 is a reproduction of thewriters case. Os Sustentaculi. This is a small, wedge-shaped bone which comprises the upperposterior end of the sustentaculum tali. Itssize is about 10 mm. in a transverse direc-. FlG. 3. Trigonum. age and separated by a joint cavity whichma\ be continuous with the cavity ot theposterior astragalo calcaneal may be fused with the astragalus, or theonly evidence of its original independencemax be a groove on the under articular sur-face which separates the posterior articularsurface of the calcaneus into pars propriaand pars trigona. In size, the trigonum isusually from 15 to 22 mm. in a transversedirection, and from 10 to 15 mm. in boththe sagittal and vertical directions. For presentation in the roentgenogramthis bone probably has the most favorableposition 01 all the supernumerary a lateral view of the ankle it will be foundat the posterior edge of the astragalus,bordering on the superior surface of thecalcaneus | Fig. 51. Astragalus Secondarius. This is a small,oval ossicle lying above and behind thehead of the astragalus, near the anteriorportion of the
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