Diseases of the nervous system / edited by Archibald Church.

Date:
1908
Catalogue details

Licence: In copyright

Credit: Diseases of the nervous system / edited by Archibald Church. Source: Wellcome Collection.

    134/1256 page 106
    If we trace the radiation of the corpus callosum into the hemispheres we see it distributed to various regions of the cortex; the anterior portion passes over the anterior division of the lateral horn to the frontal lobes; fibers of the corpus callosum which pass to the occipital lobe encircle the posterior horn from above; these are called the forceps major; others which do not run so far backward as laterally pass to the outer side of the posterior horn in the temporal lobes, and are known as the forceps minor. Some of the coordination fibers of the cerebrum do not pass through the corpus callosum but into the anterior commissure. We know from the macro- scopic anatomy of the brain that this passes from one side to the other quite anteriorly in the ventral portion of the third ventricle, in front of the crus of the fornix and under the septum pellucidum. It lies at the same time under the head of the corpus callosum. In the hemispheres the fibers radiate below the corpus striatum, quite close to the floor of the brain, and above the substantia perforata anterior, also posteriorly and downward as far as the posterior parts of the temporal lobes. Here they join the cortex of the hippo- campus major, and appear to form a coordination system for the sense of smell. A few fibers apparently enter the tractus olfactorius (olfactory lobe). There are a few other small commissure systems (commissura mollis and posterior, lyra Davidis) the importance of which I shall not discuss. Besides the association and projection fibers of the cortex of the cerebrum there are numerous projection fibers in the corona radiata, and these run caudally to the trunk ganglions (nucleus caudatus and corpus striatum), to the thalamus (inter-brain), directly downward to the middle brain (corpora quadrigemina), or to the medulla oblongata and the spinal cord. The second motor neuron and the third sensory neuron are known to be important parts of these projection fibers, but the origin and course of many of the fibers from this tract are still unknown and their function still obscure. I shall now leave the fiber systems of the cerebrum, and pass to the con- sideration of «tracts in the caudal portions of the brain. The trunk ganglia (lenticular nucleus) and the thalamus are connected by a closed tract, the lower part of which is surrounded by the internal capsule. This is the ansa nuclei lentiformis. It forms the three links of the lenticular nucleus; its function is still unknown to us. I must also call attention to the fasciculus longitudinalis posterior (Figs. 94—98), a bundle of longitudinal fibers which may be traced caudally from the region of the corpora quadrigemina far down into the medulla. It is invariably situated in the sagittal plane of the lemniscus tract, extending dor- sally beyond it as a closed round bundle. During its course it constantly gives off fibers to the cranial nerve nuclei, and appears to form for these an asso- ciation center, made necessary by their complicated and numerous coordinate functions. In conclusion I must mention a net-like layer (fibers and nerve-cells combined) which may be followed from the most caudal portion of the medulla through the pons to the tegmentum of the cerebral peduncles. This tract, formerly designated the substantia reticularis (Figs. 91, 93-96), has been characterized by Bechterew as the central tegmental tract. Its function is unknown. In the medulla and pons it usually lies laterally and above the lemniscus; it disappears in the region of the corpora quadrigemina.
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