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NUMBER 89 269
C
Psp Lep
FIGURE 3.—Interrelationship of parts of the pseudotemporalis muscle and epipterygoid or its apparent remainder
(lig. epipterygoideum): A,B, Tuatara, Sphenodon punctatus (Gray); C,D, tinamou, Eudromia elegans.
Ept=epipterygoid; Lep=ligamentum epipterygoideum; Ls=laterosphenoid; Ps=undivided M. pseudotemporalis;
Psp=M. pseudotemporalis profundus; Pss=M. pseudotemporalis superficialis; Q=quadrate. (A,B, after
Dzerzhinsky and Yudin, 1979; C,D, after Dzerzhinsky, 1983.)
panica. In adult Tinamiformes (e.g., Rhynchotus) these relations
are obscured by later ossification, but they are quite clear
in young Eudromia elegans Geoffroy Saint-Hilaire (Dzerzhinsky,
1983). Due to the occipito-mandibular ligament, the pterygoid
muscle as a whole can act similarly to the retractor, but in
contrast to it, via the mandible.
2. M. pseudotemporalis (part of the internal mandibular adductor)
applies a retractory force to the mandible, and the force
is transferred to the palate via the pterygoid muscle. In Sphenodon
and lizards (Figure 3A,B), M. pseudotemporalis is undivided
and originates mainly from the epipterygoid. In birds, the
epipterygoid would limit the mobility of the quadrate,
so it either has been replaced by a flexible ligament, as
in tinamous (Figure 3 C,D; Dzerzhinsky, 1983), or has
been completely reduced. Consequently, the pseudotemporalis
muscle has been divided into two portions,
FIGURE 4 (right).—Contraction effect of the pseudotemporalis profundus
muscle in the skull of the Common Raven, Corvus corax
Linnaeus. APsp=immediate force; A=final force transferred to the
braincase via the quadrate bone; Q=quadrate; Sq=squamosum.
originating from two ends of the former epipterygoid. M.
pseudotemporalis profundus originates on the tip of proc. orbitalis
quadrati, and M. pseudotemporalis superficialis originates
on the front wall of the braincase. M. pseudotemporalis
profundus produces a retracting force rather effectively, irrespective
of the particular direction of its fibers, because the resulting
force is transferred to the braincase very caudally,
through the quadrato-cranial joint (Figure 4). The main part of
M. pseudotemporalis superficialis is well developed in paleognaths
and occupies a considerable area of the temporal surface
of the braincase (Figure 6A). But even here it passes rather