Diseases of the nervous system .. . regard to the secondari/ optic tract, we must assume that the externalgeniculate body, 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 directJy to the cortex of the hrain 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, inclu
Diseases of the nervous system .. . regard to the secondari/ optic tract, we must assume that the externalgeniculate body, 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 directJy to the cortex of the hrain 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 tJiird sensory neuron which is now to be de-scribed. (3) THE THIRD SENSORY NEURONS 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 tliird sensoryneuron in addition to the two neurons we have discussed. The marked devel- Stratum zonale. Lemniscus lateralis Radix fiescendeiis(mesencephalica)n. trigemini Nucleus lemniscilateralis Sulcus lateralismesencephali Lemniscusmedialis Nucleus colliculi inferiores— Stratum griseum centrale cerebri(Sylvii) Lemniscus tract tothe basis pedunculii Fig. 97.—Traxsverse Sectiox xHRorcH the Lpper Margix of the Pox;RioR Corpora Quadrigemixa. (After Toldt.) Nucleus n. troch-learis Fasciculus lon-gitudinalismedialis Decussatiobrachii con-junct ivii ^ Recessus pos-terior (Tarini) Fibrce pontis su-perficiales AXD THE POSTE- 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 wavs with others in the sensorv tract. 98 HISTOL
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