In some of the experiments, instead of actual removal of a portion of cortex, a subcortical lesion was made, and the piece left in situ. The results yielded differed in no way from those furnished by the more usual method of removal. Control experiments, in which the surface was merely exposed, were also performed. In all, the results of experiments upon thirty brains were investigated, fifteen of which were monkeys and a like number marmoset brains. Through these, (a) (3.) (c) (d) Fig. 1.-Showing tracings of lesions from four of the marmoset brains, viz. marmosets V., VI., VII., VIII. sections were made in various directions, horizontal, coronal, and oblique. Before cutting, photographs or tracings of the lesions, or both, were made. RESULTS OBTAINED. Degenerated fibres were ascertained to exist in the following tracts and fibres: 1. Association Fibres.-In the first instance short association fibres connecting the removed area with adjacent convolutions or portions of cortex were found degenerated. But, in addition, longer association tracts were also found to present the same change. One of these was the inferior longitudinal fasciculus conveying degenerated fibres into Fig. 3.-Horizontal section through the brain of marmoset vi. at the level of the upper part of the internal capsule; showing sites of degeneration: d. 1. internal capsule, side of lesion. d. 2. inferior longitudinal fasciculus. d. 3. tapetum, side of lesion. d. 4. tapetum, opposite side. d. 5. corpus callosum. d. 6. internal capsule, opposite side to lesion. the occipital lobe (see d. 2. figs. 3 and 4). The other conveyed similar fibres to the parietal lobe-parieto-temporal fasciculus. These results are confirmed by recent observations of Pusateri1, who found degenerations in these tracts after removal of portions of Munk's auditory sphere in cats. It must, I think, therefore be unquestionably accepted that the inferior longitudinal fasciculus is mainly, if not wholly, an association link between the occipital and temporal lobes. This, the usually accepted view, has recently been contested by Flechsig, who regards it as a projection bundle, descending from the occipital lobe. It has, however, on the other hand received confirmation from researches by Sachs into degenerations following softening of circumscribed areas of the cortex. 2. Commissural Fibres :— (a) Corpus callosum.-In every case degenerated fibres were traced over the ventricular cavity towards the corpus callosum, across the posterior half of which they passed to reach the opposite side (see d. 5. fig. 1). In this commissure, they were found mostly to occupy the lower half of the vertical section. Having gained the opposite side, a number were seen to bend downwards and radiate into the cortex of the opposite temporal lobe. Some fibres turned forwards into the internal capsule. These will be referred to later. But fibres of another set were also traceable from the seat of the lesion towards the region of the corpus callosum at its hinder part. Here they entered the bundle of fibres known as the tapetum (see d. 3, fig. 3), and at once separated into two groups. One of these remained on the side proximal to the lesion, and passed back into the occipital lobe, forming a layer immediately outside the posterior horn of the lateral ventricle. The other crossed over in the corpus callosum, and was found in the tapetum of the opposite side, along which its fibres were traced backwards and downwards into the occipital lobe, forming here also a layer placed closely external to the posterior horn (see d. 4, fig. 4), and internal to the so-called optic radiations of the white centre. In this way a communication is established between a given area of temporal cortex and the surfaces of both occipital lobes. 1 Pusateri, E., " Contrib. allo studio dell' origine del fascio pedunc. di Türck e del fascio long. infer." Il Pisani, s. 141-154. 2 Flechsig, P., "Die Localisation d. geistigen Vorgänge, insbesond. der SinnesEmpfindungen d. Menschen." Leipz., 1896. 3 Sachs, H., Ueber Flechsig's Verstand-Centren." Archiv f. Mik. Anat., B. 48, p. 550-572. Some light is also thrown upon the constitution of the tapetum, concerning which a good deal of difference of opinion exists amongst : Fig. 4.-Horizontal section from same brain as fig. 3 at a lower level: d. 1., d. 2., d. 4., as in fig. 3. d. 6. degenerations extending out into opposite temporal lobe. d. 8. in external capsule. cerebral investigators. Wernicke believed it to be a set of fibres 1 Wernicke, Lehrbuch d. Gehirnkrankeiten. Leipzig, 1881. passing from the corpus callosum into the internal capsule. Dejerine', however, identifies it with the occipito-frontal fasciculus of Forel and Onufrowicz; but while denying that it receives any fibres from the corpus callosum, or contributes any to the internal capsule, admits that it is made up of fibres from two different sources. Where the second set of fibres originates Dejerine does not state. Mingazzini3 corroborates the view that the tapetum contains two sets of fibres, one of which belongs to the fasciculus occipito-frontalis; the other is furnished by the corpus callosum. Dotto and Pusateri1 have also found that the corpus callosum contributes fibres to the tapetum. My own results fully substantiate this latter view, and further show at least one source from which the callosal fibres come. They do not lend any support to the belief that fibres of the tapetum descend into the internal capsule. To reach from the (b) Anterior commissure.-In all cases where the lesion of the temporal cortex was extensive, marked degeneration was found in the anterior commissure. Here the fibres occupied the inferior half of its vertical section (Pars corticalis) (see d. 3. fig. 5), and passed across to the opposite side, where they bent outwards and backwards, to end in the lower and front part of the cortex of the temporal lobe. the anterior commissure, these degenerated fibres coursed seat of lesion, along the external capsule (see d. 8, fig. 4). But all of those found in the external capsule did not enter the anterior commissure. Many descended to the anterior and lower part of the temporal cortex on the side of the lesion. Through the external capsule and anterior commissure another bilateral connexion is thus established between the cortex of the temporal lobe and both hemispheres, comparable to that formed in a posterior direction by the fibres of the tapetum. (c) Fornix. In a small number of the brains examined, degenerated fibres were detected in the body of the fornix (see d. 6. fig. 4). They probably belonged to the set of fibres described by authors under the name of fasciculus pericavitarius medialis. They were traced forwards 1 Dejerine, J., Anatomie des Centres Nerveux. Tome 1, p. 760. Paris, 1895. 2 Forel, "Fall von Mangel d. Balkens in einem Idiotenhirn," Tagebl. d. 54. Versamml. deutsch. Naturforsch. u. Aertzte in Salzburg, 1881. 3 Mingazzini, G., "Osservaz. Amat. intorn al corpo callose e ad alcuno formaz che con esso hanno rapporto." Ricerch. lab. di Anat. Norm. Univ. Roma., vol. p. 5-28. vii., 4 Dotto and Pusateri, "Sul decorso delle fibs. del corp. callos. e del psalterum." Rivist. di patol. Nerv e ment. II., 2, 1897. |