THE CEREBRAL PEDUNCLE AND THE PYRAMID

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Abstract
In this study the cerebral peduncle and the pyramid in the ferret and the goat were studied. In the ferret the fibre-content of the peduncle and of the pyramid were examined at 4 levels and it was demonstrated that in the same animal both sides did not differ significantly in total fibre-content and in fibre-pattern. Those of different animals, however, did differ considerably in total fibre-content though not in fibre-pattern. The percentages of fibres leaving the levels between the peduncle and the pyramid were computed. More than half of the fibres left this system before the caudal end of the pons was reached. Cortico-mesencephalic and pontine fibres in the different animals differ considerably in amount, the pontine fibers in one animal being very numerous. The other fibres did not differ so much and the cortico-bulbar amounted to about one-third of the cortico-spinal fibres. The cortico-mesencephalic contingent contained somewhat more fine and the bulbar somewhat more coarse fibres than the averages of the peduncle. In ablation experiments it was proved that the medial half of the peduncle and the cortico-bulbar and spinal fibres arose exclusively from the posterior sygmoid and coronal gyrus with some fibres from the anterior sygmoid gyrus. The lateral half of the peduncle arises from the parietal, temporal and occipital cortex. Both halves of the peduncle contain about the same number of fibres, and as to fiber caliber they are similar. Only the most dorso-lateral part of the peduncle in level 1 contains a surplus of fine fibres. The lateral half ends entirely in the mesencephalon and the pons; only relatively few fibres from the medial half end there. A premotor frontal portion comparable to Arnold''s tract in the primates could not be found. In the goat a cortico-bulbar tract separated from the peduncle, defined by Bagley [ 1922] in the sheep, was found to originate from the medial half of the peduncle in the high mesencephalon. The medial half of the peduncle, the pyramid and Bagley''s bundle consist of fibres from the precentral area, and both sygmoid gyri, with only a few fibres from the frontal area and the coronal gyrus. The lateral half consists of fibres from the parietal, temporal and occipital areas with very few from the coronal gyrus. The peduncle of the ferret and the goat is comparable to that of primates minus the frontal contingent. The non-pyramidal fibres within the peduncle are not to be considered as going exclusively to the basal pontine nuclei. Arnold''s fronto-pontine tract apparently occurs only in primates.