Somatotopic representation of the laryngeal motoneurons in the medulla of monkeys.

Following HRP injection into the cricothyroid (CT), posterior cricoarytenoid (PCA), thyroarytenoid (TA), lateral cricoarytenoid (LCA), and the interarytenoid (IA) muscles, most of the labelled neurons were observed ipsilaterally in the nucleus ambiguus (Amb), whereas a few labelled cells were also recognized in the reticular formation. The labelled cell column for CT extended from a level near the rostral end of the inferior olivary nucleus (IO) to a level caudal to its middle part. The labelled cell columns of PCA, TA, LCA and IA were located between the level rostral to the middle of IO and that of the caudal end of IO. These findings agree with our previous studies on cats. However, in the transverse plane, CT motoneurons were arranged in annular fashion around the Amb. Motoneurons of PCA were located in the medial part, those of TA in the lateral part, and those of LCA and IA in the middle part of the Amb. These findings differ from our findings in cats, described elsewhere.