A degeneration study of the course and extent of the pyramidal tract of the opossum

The pyramidal tract was studied in 12 adult opossums. The method employed consisted of unilateral ablation of the motor cortex followed by selective staining of the resulting fiber degeneration with Nauta's silver technique. The results showed that in the upper part of its course the pyramidal tract followed a course similar to that found in other mammals. It descends in the internal capsule, cerebral peduncle, basal pons and the pyramids of the medulla oblongata where it decussates. It then continues to descend in the dorsal funiculus through the entire cervical cord. In the spinal cord fibers appeared to terminate among neurons at the base of the dorsal gray column. No degeneration could be traced directly into cranial and spinal nerve nuclei.