Boyer diss 2009 1046..

The g3 groove stems from an area on the promontorium that is slightly
anteromedial to the oval window and leads to the medial side of the s2 septum. Its course
is thus more medially directed than that of the g2 groove. It does not appear to be related
to the internal carotid plexus because it approaches the s2, not the anterior septum, as in
other mammals. It also seems unlikely to represent any other nerve bundle such as the
lesser or greater petrosal nerves, because it is medial to the g2 groove, which apparently
represents the internal carotid plexus. MacPhee (1981) illustrates the lesser and greater
petrosal nerves lateral to the internal carotid plexus route in euprimates, treeshrews and
macroscelideans. Apparently in lemuroids, lorsoids and treeshrews of MacPhee (1981)’s
sample a small vein follows the medial secondary septum. Thus, it seems most
parsimonious to conclude that s2 represents the equivalent of the medial secondary
septum and g3 primarily held a small vein. However, grooves connecting the g3 and g4
suggest that tympanic plexus fibers ran along the g3 route as well.
The g4 groove is often closely associated with the groove and foramen for the
tympanic canaliculus. This is consistent with it representing branches of the tympanic
nerve, as suggested by MacPhee et al. (1983) for N. gidleyi 17388. The majority of these
nerves fibers appear to have reached the lateral side of the pars cochlearis using either an
intrapetrous route on some ears, or subpetrous route on others, as indicated by the
asymmetrical morphology of N. gidleyi AMNH 17388. On the right side of AMNH
17388 there is no evidence of a foramen located on the septum of the cochlear
canaliculus, leading into the promontorium, but the g4 groove appears well-developed,
thus marking a subpetrous route for the tympanic nerve (MacPhee et al., 1983: fig. 1
“s1”). The left side is differently configured. The groove and foramen for the tympanic
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