When confronted by a patient exhibiting loss or impairment of voluntary power, a clinical examiner sets about at once to determine whether the disturbance is in the muscles themselves or in the nervous system. The case history generally indicates which one is involved, and if the trouble proves to be nervous in origin, the next step is to decide whether the central or peripheral nervous system is primarily concerned. In current neurologic teaching a broad distinction is made between the paralyses resulting from lesions of the "lower motor neuron" and those due to interruption of the "upper motor neuron." The lower motor neuron has its beginning in the cells of the anterior horn and its ending in the skeletal muscles. The term upper motor neuron has reference to the pathways from the cerebral cortex conveying volitional impulses, directly or through intermediate neurons, to the anterior horn cells of the spinal