Motor function and the corticospinal tracts in the dog and raccoon

Following unilateral somatomotor cerebral cortex ablation in three raccoons and ten Beagle dogs similar functional deficits of hypotonia, hypokinesia and dysmetria limited to the side opposite the lesion were observed in both species. Only in the raccoon was a loss of digital manipulative ability of the contralateral forepaw observed. The Nauta‐Gygax method was used to trace corticospinal projections into the grey matter of the spinal cord. In both species preterminal degeneration was found ipsilaterally and contralaterally in Rexed's laminae V, VI, VII and VIII. Furthermore, in the raccoon preterminal corticospinal degeneration was followed into the dorsal portion of contralateral lamina IX at the level C7–8. Although direct corticospinal projections to motoneurones of lamina IX occur in greater quantity and in increasing quantity with increasing complexity of digital abilities among the primate species, it appears that such connections are not limited phylogenetically to primates and probably are correlated with the ability of a species to manipulate the digits. Comparison of these anatomical findings with those reported for the cat revealed a progressive ventral shift of corticospinal terminations in ventral horn neuronal groups from cat to dog to raccoon, specifically into lamina IX in the raccoon. No single pattern of corticospinal terminations appears typical for the Order Carnivora. Data on dogs varying in age from one month to adult support the suggestion that there is a direct correlation between some motor cortex functions and postnatal maturation of corticospinal connections.