Fig. 8. A–C: Lateral flesh reconstruction of neck and jaw musculature
of Tyrannosaurus rex (A), Allosaurus fragilis (B), and Ceratosaurus
nasicornis (C). Tendinous attachments are rendered as white. Neck
muscle abbreviations are as in Figure 4. B: In Allosaurus fragilis, the
novel course of m. longissimus capitis superficialis is evident. In Ceratosaurus
m. longissimus capitis profundus and m. rectus capitis ventralis
are restored as robust, based on the large size of their insertions.
M. transversospinalis capitis has a relatively small insertion on the
parietals in Ceratosarus, and this muscle is restored here as slender
compared with that in Tyrannosaurus and Allosaurus. Jaw muscle contractions
are: m. a.m.e. med. 5 m. adductor mandibulae externus
medialis. m. a.e.s., m. adductor mandibulae externus superficialis; m.
a.e. post., m. adductor mandibulae posterior; m. dep. mand., m. depressor
mandibulae; m. pt. ant., pterygoideus anterior/dorsalis; m. pt.
post., m. pterygoideus posterior/ventralis.
www.ohio.edu/people/es180210/Snively%20pdfs/snively_russell_theropod_necks.pdf
Fig. 9. Schematic dorsal reconstructions of neck muscles in large
theropods, with intervertebral muscles omitted. Most abbreviations are
as in Figure 4 (m. epi.-cap. med., m. epistropheo-capitis medialis),
and color-coding and superficial-to-deep conventions are as in Figure
7. A–C: Juvenile Tyrannosaurus rex, reconstructed from measurements
and photographs of BMRP 2002.4.1. The occiput and some cervicals
are restored after adult specimens. Tendons of m. l.c.d./t.cerv. B, right)
would insert onto the anterior epipophyses posteroventral to the origins
of m. complexus (B, left). M. l.c.d./t.cerv. is shown here overlying
these structures to emphasize the course of the entire muscle complex.
D: Adult Tyrannosaurus rex (AMNH 5027; skeleton after Paul,
1988), showing the breadth of the neck muscles (in black) relative to
other depicted theropods. E–G: Neck muscles of Allosaurus fragilis,
overlying a skeletal reconstruction of UNNM 4734 modified from Paul
(1988). One part of the m. l.c.d./t.cerv. system is shown (F), with origins
from posterior neural arches and insertions onto the posterior surfaces
of the anterior epipophyses. H–J: Ceratosaurus nasicornis, with
muscles overlying a skeletal reconstruction of USNM 4735 modified
from Paul (1988). Note the narrow insertions of m. t.cap. compared
with those in Allosaurus fragilis (E–G) and Tyrannosaurus rex (A–D). In
E–J, a ligament may have been present in the depicted locations of
m. epistropheo-capitis medialis.
The origins of m. transversospinalis capitis in Ceratosaurus
are bracketable as having been tendinous from the dorsal
surfaces of the neural spines. Osteoderms, closely associated
with the neural spines in Ceratosaurus nasicornis
(USNM 4735), resided within the skin and superficial fascia
covering the muscle, and would have been dorsally displaced
by it during life. This interpretation could be falsified
or complicated if histological evidence points to close
connection between the osteoderms and neural spines.
There are several nonexclusive candidates for the insertion
of m. transversospinalis capitis. Unlike Allosaurus
and tyrannosaurids, Ceratosaurus lacks a broad nuchal
crest that would support a large tendinous insertion.
Instead, the parietals of Ceratosaurus slope ventrolaterally
on either side of a caudally rugose, posterior projection
of the supraoccipital (like that present in Allosaurus).
The parietals may bear a midline, dorsal posterior projection
above the supraoccipital, as do those of Ceratosaurus
magnicornis (MWC 0001), or grade posteroventrally into
the supraoccipital (the large Ceratosaurus sp. A: BYU 881/
12893). The posterior projection, consisting of either configuration
of bones, is similar to the parietal eminence identified
in the abelisaurid neoceratosaurians Majungatholus
atopus and Carnotaurus sastrei (Sampson et al., 1998). It is
possible that m. t.cap. had a medial insertion on the posterior
projections of the parietal and/or supraoccipital, and a
lateral insertion onto the ventrolaterally sloping ridges of
the parietals. The axis (C2) of Ceratosaurus has a strong
medial ridge (UUVP 1053), the prespinal ridge of Madsen
and Welles (2000), that corresponds with the supraoccipital
projection. It is, therefore, possible that a C2-supraoccipital
ligament spanned the gap between these elements, and that
the insertion of m. t.cap. was limited to the parietals. Alternately,
amuscle similar tom. epistropheo-capitismedialis of
crocodilians may have inserted here, originating from the
medial portion of the axial neural spine. In either case, this
mediolaterally concentrated insertion of m. t.cap. was more
like that of the narrow tendinous insertion seen in crocodilicrocodilians
and birds than the broad insertion of Allosaurus and
tyrannosaurids.
The insertion of m. t.cap. in Ceratosaurus was dorsal to
the occipital condyle, in a position enabling it to effect dorsiflexion.
The lever arm does not appear to be relatively
as long as that of Allosaurus and tyrannosaurids.
