The localization, in the nucleus ambiguus of the rabbit, of the cells of origin of motor nerve fibers in the glossopharyngeal nerve and various branches of the vagus nerve by means of retrograde degeneration

The glossopharyngeal nerve and the vagus nerve or its branches were cut individually or in various combinations in different rabbits. In two animals the cricothyroid muscle of the larynx was dissected away. The distribution in the nucleus ambiguus of the neurons of origin of motor fibers in the various nerve branches was deduced from the retrograde degeneration observed in these cells after the appropriate branch had been cut or muscle had been removed. The part of the glossopharyngeal nerve associated with the nucleus ambiguus was found to arise from a compact mass of cells lying level with, but ventrolateral to, the rostral tip of the principal column of the nucleus, forming the rostral extremity of the medial column. The remainder of the medial column was shown to give rise to axons innervating the cricothyroid muscle. The principal column contains a group of cells innvervating the pharynx and soft palate and a group innervating the esophagus, but there was considerable rostrocaudal overlap between these two groups. Some evidence is presented showing that the cells for the cervical esophagus are not clearly separated rostrocaudally from the cells for the abdominal esophagus. The cells of the diffuse formation innervate the intrinsic muscles of the larynx excepting the cricothyroid muscle.