The studies were performed on 24 young, adult dogs. In 16 of the animals sections were made of the descending ramus of the hypoglossal nerve and of the stem of the hypoglossal nerve at various levels: at the base of the skull (superior hypoglossectomy), proximally from the descending ramus (middle hypoglosectomy), and at the entrance to the tongue (inferior hypoglossectomy). Phantom operations were performed in 4 animals and material from 4 others (not operated on) was used for control purposes. The post-operative survival rate ranged from 10 to 29 days. In all 4 cases rostral spinal cervical ganglia were collected. In half of the cases the materials were stained with cresyl violet and further quantitative and qualitative studies of retrograde neuronal changes were performed. The remaining half of the material, prepared with Gomori method on acid phosphatase, was subject to statistical analysis of the degree of acid phosphatase activity. The increase or decrease in number of neurons of definite degree of activity was taken as an index of the increase or decrease of enzymatic activity. As a result of transection of the hypoglossal nerve and its descending ramus, in cresyl violet material, qualitative and quantitative degenerative changes were found in dorsal root ganglia C1 to C3 on the operated side. It was also found that corresponding to the tigrolytic changes in the neurons of the above mentioned ganglia there was an increase of activity for acid phosphatase. The same kinds of changes were found in the spinal ganglia C2 and C3 after transection of the hypoglossal nerve at the entrance to the muscles of the tongue. These results lead the authors to suggest that the tongue motor apparatus receives afferent innervation from neurons locates homolaterally in spinal ganglia C2 and C3.