The motor cortex and pyramid tract in the raccoon (Procyon lotor Linn.)

Abstract

The raccoon is a very intelligent animal and, as one would expect, relatively to the size of its body, it possesses a large brain with a highly convoluted cerebral cortex. Little appears to be known, however, about its cortical topography or the fiber tracts of its central nervous system.

The present note refers to the experimental localization of the motor areas and the subsequent tracing of the pyramid tract by the method of ablation and secondary degeneration. Five full-grown specimens were obtained. The cerebral cortex was exposed on the left side, under ether anesthesia, the motor areas were localized both by the bipolar and unipolar methods and then removed. The wound was closed and the animal allowed to live for about two weeks when the left hemisphere was exposed and explored in the same way before the animal was finally dispatched by an overdose of ether. The brain and spinal cord were removed and treated by the Marchi method.

The region from which muscular responses were obtained is relatively large and well defined. It occupies the whole free surface of what may be termed the post-cruciate convolution, extending from the mesial border of the hemisphere to a little way beyond the lateral extremity of the cruciate sulcus. Unless when the current was comparatively strong, no movements were obtained from the cortex in front of the cruciate sulcus. From the mesial border lateralwards the order of the responsive areas was as follows: anus, tail, hind limb and digits, body, fore-limb and digits, head and eyes, and face, mouth and tongue, the last curving forwards around the lateral extremity of the sulcus. The movements were readily elicited and the areas well defined but there was always some overlapping at the margins.