. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. OH scap â ⺠OH clav. Figure 3. The hyobranchial apparatus of Varanus exanthematicus, in ventral (top row) and lateral (bottom row) views. Force vectors (gray arrows) show the sites of insertion and lines of action of the hyobranchial muscles, as measured in dissected specimens. (A) The hyoid in its expanded configuration; contraction of musculi (mm.) mandibulohyoideus and omohyoideuswill result in hyoid compression. Constrictor colli and intermandibularis are not shown, because they do not insert directly on the hyoi
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. OH scap â ⺠OH clav. Figure 3. The hyobranchial apparatus of Varanus exanthematicus, in ventral (top row) and lateral (bottom row) views. Force vectors (gray arrows) show the sites of insertion and lines of action of the hyobranchial muscles, as measured in dissected specimens. (A) The hyoid in its expanded configuration; contraction of musculi (mm.) mandibulohyoideus and omohyoideuswill result in hyoid compression. Constrictor colli and intermandibularis are not shown, because they do not insert directly on the hyoid. (B) The hyoid in its compressed configuration; contraction of the branchiohyoideus, sternohyoideus, and mandibulohyoi- deus III will result in hyoid expansion. Abbreviations: ap, anterior process; bh, basihyoid; cb, ceratobranchial; ch, ceratohyal; clav, clavicular; Ip, lingual process; scap, scapular; others as in Figure 2. sidering their insertion sites on the hyoid apparatus (Fig. 3), the patterns of their EMG activity, and the kinematics of the hyoid elements during each gular pump cycle. Gular expansion results from the coor- dinated activity of the sternohyoideus, branchiohyoideus, and mandibulohyoideus III. The sternohyoideus pulls the cerato- branchial in a caudoventrad direction, giv- ing it a more vertical orientation. This ac- tion tends to retract and depress the ba- sihyoid, while pointing the lingual process ventrad. With the ceratobranchial stabi- lized by the sternohyoideus, the bran- chiohyoideus tends to abduct the anterior process and retract the ceratohyal. How- ever, the proximal end of the anterior pro- cess pivots about the basihyoid, and the ceratohyal has its distal end anchored to the lower jaw by the mandibulohyoideus in. The broad, loose nature of articulation between the ceratohyal and the anterior process allows sliding to occur between these two elements. Thus, as the anterior process swings laterad, it pushes against the ceratohyal, the ang
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