. Bulletin - United States National Museum. Science. 144 UNITED STATES NATIONAL MUSEXnVI BULLETIN 247. Figure 59.—Views of left mandible, USNM 23494, of Diorocetus hiatus: a, external view; b, dorsal view; c, condyle. Abbrs.: an., angle; cm., condyle of mandible; cor., coronoid process; , gingival or alveolar foramen; , mental foramen; ipt., groove for attachment of internal pterygoid muscle. irregularly spaced (USNM 23494; pi. 51, fig. 3) or porous and rugose (USNM 16783). The internal acoustic meatus at the level of the cerebral rim is either circular or ovoidal; the rim is less than
. Bulletin - United States National Museum. Science. 144 UNITED STATES NATIONAL MUSEXnVI BULLETIN 247. Figure 59.—Views of left mandible, USNM 23494, of Diorocetus hiatus: a, external view; b, dorsal view; c, condyle. Abbrs.: an., angle; cm., condyle of mandible; cor., coronoid process; , gingival or alveolar foramen; , mental foramen; ipt., groove for attachment of internal pterygoid muscle. irregularly spaced (USNM 23494; pi. 51, fig. 3) or porous and rugose (USNM 16783). The internal acoustic meatus at the level of the cerebral rim is either circular or ovoidal; the rim is less than 8 mm. distant from the longi- tudinal crease on the pars cochlearis. The cerebral aperture of the Fallopian aqueduct (pi. 51, fig. 3) is either adjacent to the rim of the internal acoustic meatus, but having a supplemental anterior opening at the anteroextemal angle of the pars cochlearis (USNM 23494), or limited to the single anterior opening (USNM 16783) present on the pre- ceding periotic. The vestibtilar aqueduct opens into a deep ovoidal depression on the cerebral face behind and above the internal acoustic meatus. The small orifice of the cochlear aqueduct is situated ventral to the vestibular aqueduct. Measurements (in mm.) of the periotics, USNM 16783 and 23494, area as follows: Length of posterior process, distance from external wall of stapedial fossa to extremity Greatest dorsoventral diameter of periotic from most inflated portion of tympanic face oi pars cochlearis to most projecting point on cerebral face Distance between epitympanic orifice of aquaeductus Fallopii and extremity of anterior process Distance from external end of posterior process to anterior end of anterior process (in a straight line) USNM USNM 23494 16783 Right Right 89 96 42 44 130 44 40 115 Mandibles The epiphyses of most of the vertebrae accompanying the two skulls and their associated mandibles were not ankylosed to the centra and hence these two cetotheres were not physically mature. Alth
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