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.

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    follow the tract farther (Fig. 43). We then perceive that after the optic tract has passed around the cerebral peduncles (Fig. 80) it sinks dorsally into the roof of the middle brain, the characteristic portions of which are formed by the corpora quadrigemina (Figs. 81, 82). Just before it enters the middle brain it shows upon its lateral aspect a small protuberance, the corpus geniculatum laterale. A few of the fibers enter the nerve-cells, but the majority pass on in two directions. Some run through the anterior supe- rior peduncle which leads from the superior peduncle to the internal capsule, and thus enter the nerve-cells of the superior peduncle itself. The other enters the pulvinar and the stratum zonale of the thalamus opticus. The olfactory nerve receives its neuron cells in the cells of the olfactory mucous membrane. Its processes pass as fibers of the nerve of smell through the lamina cribrosa at the base of the brain, and there enter the bulbus olfac- torius (Fig. 77). Here the first division of the tract of smell terminates in cells which are situated in the gray substance in the interior of the bulbus. Much of the interest and importance of the neuron theory centers about the nature of the termination, namely, the terminal filaments which enter into the bulbus, the primary neurons of smell combined with the dendrites of the cells of the second division (see below) in the bulbus. This communication takes place in the so-called glomeruli, which form a layer in the bulbus immediately below its external white medullary covering, and which is dimly perceptible macro- scopically (Fig. 83). I shall discuss later the complicated structure of the tract of smell. (2) THE SECOND SENSORY NEURONS The peripheral neuron is always designated as the first. In describing the second sensory neuron I shall delineate the course of those nerve processes of the cells which we have learned to recognize as the terminal nuclei of the first sensory neuron, and around which they split up. Before describing the path of the sensory fibers, I must call attention to one point. In the description of the first sensory neurons I stated that many collaterals are constantly given off by the fibers. In the motor tract we recog- nize the same tendency to unite with the branches of other functionating neurons. In the sensory tract, however, especially in the first sensory neuron, the conditions are complicated by a multiplicity of collaterals and communi- cations. It will be remembered that, while giving off lateral branches (collaterals), some of the posterior roots of the spinal cord pass through the gray posterior horns, others through the Avhite posterior columns, in a manner which has been described. The fibers which pass into the posterior columns send collaterals, or even terminal distributions, into the motor anterior horn cells. These are the reflex tracts (reflex collaterals) (Figs. 68, 69, 84, 85), which unite the first sensory with the first motor neuron (Fig. 88) and which, therefore, have no central sensory continuation. Other posterior root fibers and collaterals of the gray substance communicate with cells of Clarice's columns (columna vesicalis) ; this is particularly marked in the dorsal cord, and takes place at the base of the posterior horn just where the posterior gray commissure arises.
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