THE PYRAMID TRACT AND OTHER DESCENDING PATHS IN THE SPINAL CORD OF THE SHEEP

Abstract

1. The sheep has a comparatively small pyramid tract, the fasciculi of which degenerate as a result of lesions in the motor area, previously found to be located in the superior frontal gyrus. The greater part of the fibres are of fine calibre, and the majority decussate in the lower part of the medulla oblongata and in the first cervical segment of the spinal cord. By the Marchi method they can be traced into the reticular formation at the base of the dorsal horn, among the lateral horn cells and those of the dorsal part of the ventral horn. The homolateral fibres have a similar course. 2. The tract cannot be followed beyond the first cervical segment. 3. An uncrossed ventral cortico‐spinal tract is not demonstrated. 4. Experimental lesions in the lower part of the medulla oblongata and in the spinal cord show that there are two well‐developed descending paths. A. One, in the dorsal part of the ventro‐lateral column, extends into the sacral region. It is made up of coarse fibres, and many collaterals are given off to end amongst the cells of the lateral horn and those of the dorsal part of the ventral horn. From its relations it probably represents the rubro‐spinal tract described in some other animals. B. A large ventro‐lateral path, with coarse fibres, can also be followed into the sacral segments. It is directly connected with the ventral born cells. The progressive decrease of both tracts is greater in the limb than in the trunk regions. 5. Little, if any, motor disturbance follows from cortical lesions. But when a considerable proportion of the fibres of one of these other paths is interrupted partial paralysis invariably results, from which the animals do not entirely recover in a fortnight. © 1911 The Physiological Society