FIG. 5 in The Serrialis Bone, Interparietals, "X" Elements, Entotympanics, And The Composition Of The Notoungulate Caudal Cranium

FIG. 5. Oldfieldthomasia cf. debilitata AMNH-VP 28600, right hemicranium, parasagittal sections (after Simpson, 1936: fig. 5; original magnification, cited as natural size); rostral to right. This plate includes the only section illustrations of elements Xa and Xp in Simpson's paper (ss. 10, 15, 20, and 23; cf. comparable virtual parasagittal sections in fig. 6). Neither of these putative elements passes tests for recognizing independent ossifications; see text and appendix 1. Key (Simpson's nomina in parentheses, if different from usages preferred here; periods in original omitted): caf, facial canal (canalis facialis); cpg, retroarticular canal/foramen (postglenoid canal); crty, crista tympanica; cty, tympanic cavity; ets, epitympanic sinus; fcbr, cerebral fossa; fsmp, stylomastoid foramen (foramen stylomastoideum primitivum); fg, glaserian fissure (fissura glaseri); fpg, retroarticular canal/foramen (postglenoid foramen); fpn, aditus of epitympanic sinus (foramen pneumaticum); fsm, stylomastoid foramen; fv, venous foramen; fvpl, posterolateral cerebral venous foramen; mae, external