Localization of motoneurons innervating the stylohyoid muscle in the monkey, cat, rabbit, rat and shrew

The distribution of motoneurons innervating the stylohyoid muscle was examined in the Japanese monkey (Macaca juscata), cat, rabbit, rat and house musk shrew (Suncus murinus) using the retrograde tracing method of horseradish peroxidase. The enzyme was injected into the stylohyoid muscle after ligating the central cut ends of the main peripheral branches of the facial nerve supplying the superficial facial muscles, or the trunk of the glossopharyngeal nerve supplying the pharyngeal muscles. In the monkey, cat and rabbit, stylohyoid motoneurons were identified in the reticular formation dorsomedial, dorsal or rostrodorsal to the main facial nucleus, and in the dorsomedial or dorsal border region, central part and ventral border region of the main facial nucleus. On the other hand, in the rat and shrew, stylohyoid motoneurons were found in the reticular formation dorsal or dorsomedial to the main facial nucleus and in the dorsal or dorsomedial border region of the main facial nucleus, but not in the central part and ventral border region of the main facial nucleus.