The localization of the motor neurons innervating the cricothyroid muscle in the adult dog by the fluorescent retrograde axonal labeling technique.

Injection of 4'6-diamidino-2-phenylindol 2 HCl (DAPI) into the cricothyroid muscle of the adult dog resulted in blue fluorescence of cells found exclusively in the rostral part of the ipsilateral nucleus ambiguus. These labeled neurons on the average extended 1.8 mm from the level just caudal the facial nucleus to the caudal extension. In the rostral tip of the nucleus, labeled cells were located in a scattered ventral group of larger neurons of the nucleus.