Boyer diss 2009 1046..

is roughly 2.8 mm long. Medial to the promontorium is a groove leading to a foramen
that perforates the medial process of the bulla at its medial point of termination, and one
that perforates the promontorium itself at its lateral point of termination. This feature has
been interpreted as the vestibular aqueduct by Szalay et al. (1987) but it is clearly the
tympanic canaliculus foramen and groove, as discussed for other specimens earlier
(MacPhee, 1981) (Fig. 2.21C’: 94-95). This morphology is clearly present in most other
plesiadapid specimens preserving the relevant anatomy, as discussed and illustrated
above. The hypoglossal canal appears septate, and split into two foramina, as in
Pronothodectes.
Morphology of cranial bones.– Some of the most critical information relating to
the structure of the basicranium in this specimen has been lost: What remained of the
medial process of the left petrosal when Gingerich (1976: Pl. 8c) photographed the
specimen sometime prior to 1974 is now gone. However, a cast recently made from an
old mold housed in the MNHN, retains the medial process. This cast also reveals that
MNHN CR 125 was broken at the junction of medial tympanic process with pars
cochlearis even before the medial process was lost (demonstrating that this specimen was
never substantially better preserved than the Pellouin skull anyway).
The promontoria of MNHN CR 125 conform well to the description by Gingerich
(1976). As noted above, however, neither the posterior carotid foramen nor the laterally
positioned g1 groove for the internal carotid plexus has been photographically illustrated
previously. Figure 2.21B shows this morphology. Unlike other P. tricuspidens
promontoria (see below) and unlike many other plesiadapid petrosals (see above),
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