Identification of the phrenic nucleus in the cat as studied by horseradish peroxidase bathing of the transected intrathoracal phrenic nerve.

Horseradish peroxidase bathing of the transected intrathoracal phrenic nerve was done to identify the exact distribution of neurons of the phrenic nucleus in the cat. Retrogradely labeled neurons were observed in the ipsilateral ventral horn from the lower one-fourth of the 4th to the lower end of the 6th cervical segment. In the 4th segment, labeled neurons were found at the medial part of the ventrolateral cell group. Caudalwards, the neurons shifted from lateral to ventromedial locations and, in the 6th segment, the neurons merged into the lateral part of the ventromedial cell group.