Course and termination of the pyramidal tract in the pig.

To study the pyramidal tract in the pig, the motor cerebral cortex of one side was defined electrophysiologically and subsequently excised. The animals operated were killed after 7, 11 and 14 days, and the cerebral hemisphere of the operated side, brain stem and spinal cord were removed for histological examination. The pyramidal tract proved to run ipsilaterally as far as the oral extremity of the 12th cranial nerve nucleus. The decussation, which exhausted itself almost completely at the level of the rostral extremity of the 1st cervical metamere, started here. After the limit just mentioned only rare isolated fibres were visible. Along its course, the pyramidal tract sent a small number of axons to the ipsilateral and contralateral nucleus of the 7th cranial nerve, while the fibres running from the opposite side to the reticular formation and to the hypoglossal nerve nucleus, cuneatus, gracilis and trigeminal spinal tract nuclei were more numerous.