. Diseases of the nervous system . the anterior corpora quadrigemina, and the pulvinar of thethalamus neurons of the second division develop from the three terminal stagesof the optic tract, like those in the lemniscus. The fibrillations of the first terminal stages of this nerve, so far as weknow at present, pass directly to the cortex of the brain without ending innuclei extending toward the cauda like the fibers of the lemniscus. There-fore this higher optic tract does not correspond to the second, included withinthe temporal tract, but to that third sensory neuron which is now to be de-scr
. Diseases of the nervous system . the anterior corpora quadrigemina, and the pulvinar of thethalamus neurons of the second division develop from the three terminal stagesof the optic tract, like those in the lemniscus. The fibrillations of the first terminal stages of this nerve, so far as weknow at present, pass directly to the cortex of the brain without ending innuclei extending toward the cauda like the fibers of the lemniscus. There-fore this higher optic tract does not correspond to the second, included withinthe temporal tract, but to that third sensory neuron which is now to be de-scribed. (3) THE THIRD SEXSOEY XEUROXS The complicated mechanism of the sensory conduction tract comparedwith the motor, which is evident from this description, is explained by thefact that in man as well as in all vertebrate animals there is a third sensoryneuron in addition to the two neurons we have discussed. The marked devel- Stratum zonale Lemniscus lateral Radix descendena(mesenoephalica) n. trigemini Nucleus lemniscilateralis. Nucleus colliculi inferiores»« Stratum griseum centrale Aquaeductus cerebri (Sylvii) Sulcus lateralismesencephali Lemniscus—-]medialis Lemniscus tract tothe basis pedunculii Nucleus n. troch-learis Fasciculus lon-gitudinalsmedialis Decussatiobrachii con-junctiva •* Recessus pos-terior fossaeinterpeduncu-laris (Tarini) Fibrse pontis su-perficiales Fig. 97.—Transverse Section through the Upper Margin of the Pons and the Poste-rior Corpora Quadrigemina. (After Toldt.) opment of the anterior brain (cerebrum) in the primates, the higher stage ofconscious sensation, are probably intimately related to this. It is scarcelynecessary to state that collaterals in an unentwined web pass to other centersof other neuron groups with unknown functions, especially in the cortex of thebrain itself, and are combined in various ways with others in the sensory tract. 98 HISTOLOGY OF THE CENTRAL NERVOUS SYSTEM The third sensory neuron is combined with the second i
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