Diseases of the nervous system .. . ollaterals 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 HISTOLOGY OF THE CENTRAL NERVOUS SYSTEM The third sensory neuron is combined with the second in the cortex ofthe brain. The fibers of its origin must be sought in those nuclei in whichthe lemniscus ends (Fig. 97) and also at the terminal ends of the primaryoptic and secondary olfactory fibers which have been described. In theoptic nerve the second
Diseases of the nervous system .. . ollaterals 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 HISTOLOGY OF THE CENTRAL NERVOUS SYSTEM The third sensory neuron is combined with the second in the cortex ofthe brain. The fibers of its origin must be sought in those nuclei in whichthe lemniscus ends (Fig. 97) and also at the terminal ends of the primaryoptic and secondary olfactory fibers which have been described. In theoptic nerve the second neurons must be considered the equivalent in func-tion of the third neurons of the remaining sensory tracts (Fig. 82). The Stratum album profundumAquseductus cerebri (Sylvii) Stratum griseum centrale — Radix descendens (mesencephalica) n. trigemini Stratum zonale Stratum griseum coUiculisuperioris Brachium quadrigeminum inferius Sulcus lateralismesencephali Fasciculus lon-gitudinalismedialis Brachiumconjunctivum Substantia nigra. Basis pedunculi Tegmentum ?^Decussationes teg-men torum Fossa interpeduncular(Tarini) Fig. 98.—Transverse Section through the Upper Corpora Quadrigemina, the Teg-mentum, AND THE Crus CEREBRI. (After Toldt.) lemniscus is supposed to carry all of the second sensory neurons from thespinal cord and the medulla oblongata up to the nuclei of the nerves of themid-brain and to the thalamus. The second sensory neuron of the trigeminalnerve, certainly in the rabbit, is the only one that leads somewhat dorsallyand laterally up from the median lemniscus, chiefly through the thalamus;in man this is still uncertain. The relation of the lemniscus to the cortex of the train must now beoutlined. This is brought about by the corona radiata fibrillation which hasalready been referred to. It extends as a large projection tract into the medul-lary mass of the hemisphere which we designate as the centrum motor cortical tract also runs through the corona r
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