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.

    117/1256 page 89
    Here they receive the name lemniscus (or laqueus, formerly olivary inter- mediary layer) and pass on to the frontal region. Before following the path of the lemniscus we must return to those pos- terior root fibers which ascend in the posterior columns of the spinal cord. As has been mentioned, they extend to the medulla oblongata where they terminate in numerous cells which arise at the height of the pyramidal decussa- tion, the nuclei of Burdach’s columns and of OolPs columns (Figs. 53, 87, 91, 92). These nuclei may be traced as far as the beginning of the fourth ventricle. After this the fibers in the posterior col- umn gradually become more sparse, and finally disappear completely. From the cells of these nuclei nerve fibers originate which form the sensory neurons of the second division (Figs. 85, 87). They pass to those fibers which extend from the lateral column of the spinal cord to the median line at the so- called lemniscus (olivary intermediary layer). In order to reach these fibers those from the dorsal side of the medulla must reach a zone situated more ventrally and medially, and thus they pass in an arc ventrally and inwardly from the nuclei of the posterior columns. At the same time they all cross the median line in the u raphe,” unite with the lemniscus upon the opposite side, and with this they as- cend. Until these fibers of the nuclei of the posterior column enter the lemniscus they are called fibrce arcuatee internee (Figs. 85, 91, 92). Thus we find a second sensory crossing above the pyramidal de- cussation. All sensory fibers of the second neurons, like the motor, find their way to the brain by crossing over. Those which F™- 85.—Diagram of the Course of the „ .i i. i i „ . Sensory Tracts from the Posterior pass from the lateral columns of the spinal RooTs to the Medulla. (After Edin- cord into the lemniscus without cross- ger.) ing have passed through the anterior commissure of the spinal cord from the posterior horn of the other side, while the fibrae arcuatae internae cause the crossing of the sensory tract from the pos- terior columns which until then had not been made. Hence the second sensory neuron of the posterior roots of the spinal cord ascends to the medulla oblongata in the lemniscus on both sides of the raphe. We must trace this through the pons and the middle brain. The fibers of the second sensory neuron of the cranial nerves now unite, and, the lowest, the nucleus of the pneumogastric nerve (Fig. 87) whose cells
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