Observations on the pyramidal tract of the slow loris

The pyramidal system of the slow loris was investigated physiologically and histologically. The cerebral response to medullary pyramid stimulation was mapped and found to distribute in two separate foci, rostral to the hand and foot somatosensory foci. The tract was found to contain about 204,000 fibers at the midolivary level on one side, with about 85% of the fibers less than 2 Μm and 1% greater than 4 Μm. Calculation of the amplitude and configuration of the true antidromic response, based on the histological findings, disagreed with the observed response. The latter was found to be analogous to the rwave of the American opossum, which appears to result from intracortical pyramidal tract collateral activation of the cerebral neurons. This response is not present in the macaque monkey.