Dr. Schaffer observes that there are centripetal nerve-tracts which end in the optic thalamus, from which another neuron issues which passes to the cerebral cortex. From a case of haemorrhage of the thalamus studied by Probst, it appears that the thalamo-cortical neuron passes through the lamina medullaris externa to the side of the inner capsule, and, lying close to the ganglion lenticularis, reaches the median convolutions, the parietal lobes, and the gyrus fornicatus. Those fibres which go to the occipital lobe spring from the pulvinar and disperse in the stratum sagittale externum. Probst's results agree with those of Flechsig. According to Déjerine and Long, there is no distinct sensory system in the posterior limb of the inner capsule; the fibres which go to the cortex, as well as those going to the thalamus, mingle with the fibres of the pyramidal tract, which, beginning in the knee, spread to the retro-lenticular segment of the inner capsule. Hemianæsthesia occurs under two conditions—(1) a lesion of the thalamus opticus which may affect the ganglion in the passage of the fibres either on the bulbar or cortical side; (2) when the conducting tract between the thalamus and the cortex is affected, the thalamus remaining intact. In this case the lesion is of an extensive character.
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