CENTRIFUGAL TRACTS.
t. The efferent cortico-muscular or motor tract takes its origin in the motor region of the cerebral cortex. • Neurone I: through the internal capsule (knee and anterior two-thirds of the poste rior limb), the basis or crusta of the cerebral peduncle (middle three-fifths), the pons and the medulla oblongata.
a. as the tract of the motor cerebral nerves, to the contralateral nuclei of the motor cerebral nerves.
B. as the pyramidal tract proper, to the spinal cord—crossed as the lateral pyram idal tract, uncrossed (in the medulla oblongata) as the anterior pyramidal tract—to end around the ventral horn-cells.
Neurone II: origin within the nuclei of the motor cerebral nerves, peripheral course as the motor cranial nerves to the muscles ; or, in like manner, as Neurone II: origin in the cells of anterior horn of the spinal cord, peripheral course through the ventral roots, as the motor spinal nerves to the muscles.
2. A special motor does not exist. The speech-tract is identical with those paths, which, as part of the cortico-bulbar tract, pass from the cortical centre for the facial and hypoglossal nerves to the nuclei of the nerves necessary for speech.
3. A motor path goes to the spinal cord by way of the nucleus ruber, as follows : Neurone I: from the cerebral cortex to the nucleus ruber ; Neurone II: nucleus ruber, tractus rubro-spinalis, spinal cord ; Neurone III: spinal cord, anterior root, muscle.
4. An indirect motor path passes to the spinal cord by way of the pons and the cerebellum, as follows : frontal and occipito-temporal pontile tract—pontile nucleus—cere bellar cortex—nucleus dentatus cerebelli—superior cerebellar peduncle—nucleus ruber tractus rubro-spinalis—spinal cord—muscle (Fig. 147).
5. In addition to the above direct and indirect motor paths, others arise within the lower brain-centres and pass spinalward ; such are the tractus rubro-spinalis, the tractus tecto-spinalis and the tractus vestibulo-spinalis.