Boyer diss 2009 1046..

canaliculus are present on the septum covering the cochlear canaliculus (Fig. 2.16A-C),
but the more ventromedial aspect of the promontorium is free of any marks. Ventral to
the fenestra vestibuli, at the base of the posterior septum, a deeply incised groove stems
anterodorsally from an apparent foramen (Fig. 2.16C: g4). It seems likely that this
represents the emergence of the tympanic nerve from an intra-petrous tympanic
canaliculus route.
The g5 groove is a trough-like groove that sometimes appears as an anterior
continuation of g1. It is located dorsolateral to g2. It is quite broad and may represent
the place of formation of the main part of the tympanic plexus. The deep petrosal nerve
likely stemmed from this point to meet greater petrosal nerve, which seems to have
emerged just lateral to this groove from the hiatus fallopi (Fig. 2.40).
As mentioned above, the morphological expression of some identified grooves is
variable from specimen to specimen. It was argued that in the case of the morphology
examined here, most of this variability is not likely to reflect variability in the presence of
the soft anatomical structures these grooves are interpreted to have held. The logic
behind this is demonstrated with an example: in P. tricuspidens (MNHN CR 125) the g2
groove is absent. However, the carotid canal and g1 groove are present. Thus, the
internal carotid nerve and possibly an arterial remnant (see Chapter 5), clearly gained
entrance to the tympanic cavity. The lack of a g2 groove reflecting the “typical” course
of the internal carotid plexus to the s1 (MacPhee, 1981) is therefore not sufficient
evidence to conclude that the internal carotid plexus did not have an intratympanic
course. Given the absence of other “alternative” grooves that could plausibly represent
the internal carotid plexus across the promontorium, the most conservative interpretation
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