Previous investigators have suggested that depression of the lower jaw and the concomitant extension of the intracranial joint in the living coelacanth Latimeria chalumnae occurs by contraction of the coracomandibularis muscle. An alternative hypothesis is proposed in which posterodorsal hyoid movement accompanied by extension of the otico-occipital portion of the cranium on the vertebral column mediates mandibular depression. Movement of the hyoid apparatus, initiated by contraction of the sternohyoideus muscle, is transmitted to the lower jaw by the symplectic bone and by a strong ligament between the symplectic and the mandible. This hypothesis is corroborated both by a force analysis of the effect of coracomandibularis contraction which suggests that it functions to adduct the lower jaw, and by an electromyographic analysis of the homologous muscle in the primitive actinopterygians Amia and Polypterus.