Text-fig. 2. Metacheiromys marshii, AMNH 131777, drawing of basicranium in ventral view with isosurface from CT scans of left petrosal inserted (compare with Simpson 1931: fig. 7). Much of the mastoid exposure on the specimen's left side is damaged. Numbers 1 to 4 indicate depressions that based on the right side include a thin layer of entotympanic; 1 to 3 are between petrosal and basioccipital and 4 is petrosal only. The white arrow in the lower left passes through a canal between the petrosal

Text-fig. 2. Metacheiromys marshii, AMNH 131777, drawing of basicranium in ventral view with isosurface from CT scans of left petrosal inserted (compare with Simpson 1931: fig. 7). Much of the mastoid exposure on the specimen's left side is damaged. Numbers 1 to 4 indicate depressions that based on the right side include a thin layer of entotympanic; 1 to 3 are between petrosal and basioccipital and 4 is petrosal only. The white arrow in the lower left passes through a canal between the petrosal and exoccipital for the auricular branch of the vagus nerve. Abbreviations: abX – grooves and foramina for auricular branch of vagus nerve, as – alisphenoid, astp – alisphenoid tympanic process, bo – basioccipital, bs – basisphenoid, eam – roof of external acoustic meatus, ec – ectotympanic, en – entotympanic, eo – exoccipital, es – epitympanic sinus of squamosal, fm – foramen magnum, fo – foramen ovale, gf – glenoid fossa, hf – hypoglossal foramen, ips – foramen for inferior petrosal sinus, ljf – lateral jugular foramen, me – mastoid exposure of petrosal, mjf – medial jugular foramen, mt – muscular tubercle, mtc – musculotubal canal, oc – occipital condyle, pa – porus acousticus (hidden), pas – parasphenoid, pgp – postglenoid process, pr – promontorium of petrosal, ps – presphenoid, smf – stylomastoid foramen, sof – superior orbital fissure, sq – squamosal, tca – tympanic canaliculus, th – tympanohyal, tm – tubular external acoustic meatus.