外膝状体及び其附近の組織像

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  • Histological Image of Corpus Geniculatum Laterale and its Vicinity
  • ソト シツジョウタイ オヨビ ソノ フキン ノ ソシキゾウ エイブン

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The nerve fibres of the tractus opticus consist in their greatest majority in minute fibres, and only an extremely small minority in thick fibres. In all probability, the former originate in the small nerve cells of the nerve cell layer of the retina and the latter in the giant cells there. Among the optic fibres and especially among the small bundles of such fibres are found glial cells of two size classes, often ranged in long rosaries.<br>The tractus opticus, upon reaching the lateral geniculate body, divides in two parts, the smaller of which enwraps the body to form a capsule around it, and sending out minute bundles of fibres into the body in their further courses, enters the pulvinar thalami. The greater part of the optic fibres runs into the body from its proximal end in numerous small bundles. Besides, a rather thick branch of the tractus opticus runs right through the cranio-medial part of the geniculate body, which gives out many small bundles into the body and receives a smaller number of axons from the nerve cells in the body, finally to pass over into the brachium corp. quadrig. ant.<br>There is nothing to make the so-called griseum praegeniculatum a singular entity. It is nothing but a cranio-medial invagination of the nucleus corp. genicul. lat., bounded off by the above mentioned branch of the tractus opticus on the lateral side. It is rather to be called the accessory nucleus of the corpus than a praegeniculatum. A part of the axons of the nerve cells in the accessory nucleus goes over into the brachium corp. quandrig. ant., while the other part runs into the radiatio optica through the WERNICKE's field.<br>The zona incerta originates in the vegetative minute fibres making up a part of the pes pedunculi or the capsula interna. These fibres run around the pes pedunculi in an arcuate course, then along the medial side of the accessory nucleus and the corpus geniculatum mediale to appear in the front of the corpus Luysi, and finally to the nucleus ruber probably to come into a close relation with it. Some vegetative fibres emerging at the medial side of the pes pedunculi also partake in the formation of the zona incerta.<br>At the proximal part of the brachium corp. quadrig. ant. there are frequently found groups of nerve cells similar in nature to those in the corpus genicul. lat. This fact makes it all the more indubitable that this brachium is not only an immediate extension of the optic fibres, but also formed in part by the axons of the nerve cells belonging to the nucleus corp. genicul. lat.<br>We have to make further and more detailed examination before settling the problem of the doubtful existence of the BALADO's so-called radiatio cellularum giganticum.<br>The nerve cells in the lateral geniculate body may be classified into the two types of large and small. The large cells are far smaller in number and are chiefly found in the fifth nerve cell layer. This layer is divisible into the inner and the outer sublayers and the large cells are found in the latter in greater abundance. Between these two sublayers I have often found a thin intermediate layer of small nerve cells. Large cells are also found in sporadic arrangement in the basal part of the third nerve cell layer. The small cells are found in all the nerve cell layers and comprise cells of many variable sizes. Both the large and the small cells are pear-shaped, oval, fusiform or spherical in form and have rounded and feminine contours as is common with the sensory nerve cells in the brain stem in general.<br>The large cells are predominantly pear-shaped with their bases toward the periphery of the corpus genicul, lat. An axon from such a cell mostly emerges from its basal face, is thin but dark-staining and often runs into the capsule of optic fibres around the corpus. The short processes, 1-4 in number per cell, generally emerge from the apex of the cell, are lighter-staining but stout and branch out into numerous rami which end in sharp points.

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