Localization of the sacral parasympathetic nucleus in the dog.

The extent and location of the sacral parasympathetic nucleus was studied in 6 dogs, using light microscopy. After interruption of the pelvic nerve, chromatolytic somata were observed in thionin-stained transverse serial sections (15 mum) of appropriate spinal cord segments. Maps of the sacral parasympathetic nucleus were made by plotting the chromatolytic somata in drawings of the transverse sections of the spinal cord. The sacral parasympathetic nucleus was observed in all 3 sacral segments of the spinal cord, and in 1 dog, it also extended into the spinal cord segment Ca1. The cranial end of the nucleus was contained in the caudal one-third of spinal segment S1. The location of the caudal end was variable: it was within the middle one-third of spinal cord segment S3 in 4 dogs, in the caudal one-third of spinal cord segment S3 in 1 dog, and in the cranial one-third of spinal cord segment Ca1 in 1 dog. The densest clusters of somata of this nucleus were in the middle and caudal one-third of spinal cord segment S2. The somata, for the most part, were in the intermediolateral gray column and in the lateral funiculus. A small number of isolated somata also were in the intermediomedial gray column.