. A practical treatise on medical diagnosis for students and physicians . 323 our knowledge of this subject, destructive lesions, such as hemorrhage oraneurism, in the posterior portion of the posterior limb of the internalcapsule, or destructive lesions of the optic thalamus are usually asso-ciated with hemianesthesia on the opposite side of the body. At timestactile sense is preserved and only the pain sense lost. As a rule, how-ever, all forms of sensation are more or less affected. Motor Neurons.—The motor neurons consist of two groups, the centraland peripheral neurons. The central motor
. A practical treatise on medical diagnosis for students and physicians . 323 our knowledge of this subject, destructive lesions, such as hemorrhage oraneurism, in the posterior portion of the posterior limb of the internalcapsule, or destructive lesions of the optic thalamus are usually asso-ciated with hemianesthesia on the opposite side of the body. At timestactile sense is preserved and only the pain sense lost. As a rule, how-ever, all forms of sensation are more or less affected. Motor Neurons.—The motor neurons consist of two groups, the centraland peripheral neurons. The central motor neurons commence in the motorportion of the cortex. They then pass through the corona radiata to theinternal capsule, where they form a large band of fibres occupying the kneeand the anterior two-thirds of the posterior limb. (See Fig. 60.) Thefibres for the face occupy the knee and anterior third of this come the fibres for the arm, then those for the leg, and, finally, thefibres for the trunk. From the internal capsule the fibres pass into the •Doers. Showing the different tracts of the cord. (GOWEBS.) crura cerebri, where they lie beueath the substantia nigra, occupying aboutthe middle of each crus. The fibres for the face and cranial nerves lieinternal to those for the extremities and trunk. From here they pass tothe ventral portion of the pons, where they are broken up into smallbundles by the association of fibres of the two cerebellar reunite and form the pyramids in the anterior portion of themedulla, which decussate in the first cervical segment and pass down theeord as the lateral pyramidal columns. (See Fig. 61.) A few of theother fibres, however, do not decussate at this time, but pass downwardin the direct pyramidal columns which decussate through the anteriorcommissure of the cord at lower levels. The fibres for the cranial nervesdecussate, as a rule, in the neighborhood of the nuclei for these nerves,and by this means we are abl
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