FIG. 18 in Cranial Morphology And Phylogenetic Relationships Of Trigonostylops Wortmani, An Eocene South American Native Ungulate

FIG. 18. Cochilius volvens AMNH-VP 29651, left auditory region in slightly oblique ventral aspect. A, virtual horizontal slice through reconstructed left auditory region, with bulla digitally removed. B, same specimen, skull intact (stereopair). Bulla shifted slightly out of position post mortem, as it would normally cover caudal portion of basicapsular fenestra. Entotympanic-ectotympanic suture fully visible running parasagitally across bullar surface (see MacPhee, 2014). Key: 1, basisphenoid surface articulating with rostromedial portion of expanded bulla; 2, caudal aperture of pterygoid canal; 3, groove for greater petrosal and deep petrosal nerves; 4, transclival foramina in basioccipital; 5, groove connecting transclival foramen with small foramen in basioccipital-basisphenoid synchondrosis. In A, asterisks identify continuous basicapsular fenestra, covered by bulla in intact skull except for jugular area and foramen ovale. Dorsal wing of entotympanic (ENT) forms "medial flange," roofing over space between promontorium and medial bullar wall. For adital connection between epitympanic sinus and tympanic cavity, see figures 16 and 17.