Figure 2

Illustration of the cerato-mandibular ligament mechanism. As for the figure 1, the left oral jaws, suspensorium, opercles and hyoid bar have been removed to allow a view of right part of the hyoid apparatus in the buccal cavity. White cones indicate two muscle groups: epaxial muscles (EP) and sternohyoideus muscle (SH). In A. no movements occurs and the c-md ligament is loose. In B. Pulling on the epaxial muscle (1) induces a rotation of the neurocranium (2) provoking a rotation of the hyoid apparatus (3) which results in mouth opening (4) and in the straining of the c-md ligament. In C. additional pulling on the epaxial muscles (1) induces higher rotations of neurocranium and hyoid apparatus (2 and 3) which results, as the c-md ligament is now fully strained, in mouth closing (4). The same phenomenon of both mouth-opening and closing can be obtained by pulling along the working-line of the sternohyoideus muscle (represented in A) but there is no neurocranium elevation in this case. The angle measuring the relative movement of the two insertion points of the c-md ligament is represented by dotted lines. The angle measuring the relative movement between the neurocranium and the hyoid apparatus is represented by full lines.