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Electrophysiological studies of the rather strange, enigmatic, likely vestigial omohyoid muscle led the authors to point out the dual nature of its two bellies. Electromyographically, the inferior belly with a nearly constant activity may be opposed to the superior belly with intermittent activity. Motor nerve stimulation combined with electromyographic study demonstrated the superior belly to be supplied by the ansa cervicalis while the inferior belly is supplied by the accessory nerve. Based on these findings, anatomical studies conducted with histological examination were consistent with this double innervation.

From the anatomic element known with the man by the name of soft palatal-pharyngeal sphincter and which takes a major part in the phonation, the swallowing, the breathing, we have studied the evolutive morphology of the soft palatal-pharyngeal unity in several mammals. This unity which includes the levator palati and palatopharyngeus muscles is confirmed by the phylogenic and embryologic investigations. The comparative anatomy of the rat, rabbit, sheep and lion, allows to make obvious a evolutive line characterized by the gradual divergence of the axis of the two muscles common to the soft palatal and pharyngeal musculature, which could correspond with a phylogenic evolution.

The authors describe the soft palatal-pharyngeal unity, composed of the levator palati and palatopharyngeus muscles in the adult man, the new-born and the Saimiri. They recall the importance of the soft palatal-pharyngeal sphincter in the man's phonation. After having described the general evolution of the aerodigestive tract in the no human mammals and the man, notions of evolutive morphology of the soft palatal-pharyngeal unity are established. They are characterized by the gradual divergence of the axis of the 2 muscles forming the soft palatal-pharyngeal unity ending in the appearance met in the adult man, indispensable in view of a soft palatal-pharyngeal ability allowing a articulated language.