SUMMARY

Multi-body dynamics analysis (MDA), a 3D engineering technique, was used here as a visualisation tool to present the head and neck musculature of Sphenodon. Figure 21 displays the entire muscular anatomy of the Sphenodon head and includes all individual muscle groups covered in this paper. Alternatively, a rotating movie of the 3D Sphenodon model with all musculature is shown in Figure 22, while a rotating movie with superficial muscle groups removed is shown in Figure 23. The colour coding is consistent in all images and matches, as far as possible, that was used elsewhere (e.g., Tsuihiji 2005, 2007; Holliday and Witmer 2007; Jones et al. 2009). The detailed muscle anatomy is presented in a clear, simple manner, where muscle groups are divided into a finite number of sections, each represented by one to three straight cylinders. The ability to display a 3D representation (from any view) of colour coded muscle groups, and the option of removing or altering the transparency of specific objects means that the muscle origin/ insertion locations and muscle force lines of action can be visualised clearly.

In reality muscles bulge, wrap, and blend into tendons; they are therefore more complex in terms of their structure than represented here. Nevertheless, the presentation of muscles in this paper allows the general role of each individual muscle group to be determined based on its location, and the relative interaction between muscle groups to be inferred. For example, from Figure 14 we see that the m. Episternocleidomastoid (mEscm, red) follows on from the m. Clavicle Dorsalis (mClDo, peach) and the m. Trapezius (mTrap, purple) to form a strong collar of muscle that connects the girdle and neck with the posterior regions of the skull. We can then infer that these muscles together contribute to raising and turning/ twisting the head, as well as contributing to general head stability during activities such as feeding or locomotion. Assessing the jaw adductor muscles, we can suggest that the vertical alignment of the m. Adductor Mandibulae Externus Superficialis (mAMES, Figure 2.1) renders it well placed to move the lower jaw orthally (Olson 1961), whereas the more angled m. Pterygoideus Typicus (mPtTyp, Figure 6 and Figure 7) will contribute more towards anterior translations of the mandible.

The method of representing muscle anatomy presented here is not intended to replace more classical techniques such as line drawings for depicting observed or hypothesised muscle anatomy. The visual representations do however offer an additional and complimentary means of communicating such morphological information, and may appeal to scientists who do not have extensive experience in muscle anatomy and function.