Boyer diss 2009 1046..

and projects straight ventrally by 1.35 mm. It is lateral to the postglenoid foramen (Fig.
2.15: 63).
Petrosal.— The pars cochlearis of both petrosals are preserved, as well as some
of the septa and tympanic processes that attach to them (Figs. 2.15, 16). On the right
side, a bit of the pars canalicularis is visible. The posterior septum is either broken, or
differently configured than in other plesiadapid specimens, such that no evidence of the
g1 groove is present. Because the posterior septum actually appears fairly complete, it
may be that the internal carotid plexus did not go through the middle ear, and took a
different route in this taxon (see further discussion below). The lateral aspects of the
promontoria are obscured so that the presence of the g2 and g5 grooves and anterior
septum cannot be evaluated. The medial aspect on the right element preserves a groove
that begins near the cochlear canaliculus and arches laterally to where the posterior
septum meets the promontorium (i.e., where the g1 groove would also normally reach the
promontorium) (Fig. 2.16A-C). There is no evidence of a foramen located on the
cochlear canaliculus and leading into the promontory on this side. The groove thus has
the anatomical relationships of the g4 groove of other specimens. This is the groove
referred to by MacPhee et al. (1983) as the “s1” groove. They suggest it held fibers of
the tympanic plexus of nerves. However, as noted above, this morphology is referred to
USNM 309902 in their figure caption. The left side is differently configured. The
groove and foramen relating to the tympanic canaliculus are present on the septum
housing the cochlear canaliculus (Fig. 2.16A-C). However, the more ventromedial aspect
of the promontorium is free of any marks. That is there is no groove that matches
MacPhee et al.’s “s1” from the other side. Ventral to the fenestra vestibuli at the base of
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