Recent studies have detailed the existence of a cross-innervating branch of the extenal superior laryngeal nerve(ExSLN) to the thyroarytenoid muscle(TA). To verify and determine the nature of this additional innervation, a retrograde transport technique with horseradish peroxidase(HRP) was used. Injection of HRP to the TA, after having removed 1cm of the reccurent laryngeal nerve(RLN) innervating this muscle, resulted in retrograde labeling of the motor neurons in the nucleus ambiguus(NA) in 2 out of 6 canines. HRP labeled neurons were distributed rostrocaudally from 1.5mm rostral to the obex with about 2.5mm of caudal extension. This segment corresponded to the area of TA motor neurons from the RLN. We conclude that the TA can receive a second motor innervation from a branch of the ExSLN in some cases. This additional neural motor innervation of the TA not only has a basic interest but also may contribute to understanding phonation, as well as clinical issues in some neurological laryngeal disease.