. Diseases of the nervous system . ior horn cells with their dendrites, and of anterior roots which emerge fromthe lateral motor nerve. At the points of cervical and lumbar enlargement the number of neurons ismuch greater, because thereis a larger number of mus-cles to be supplied than isthe case in the thoraciccord. (b) The First Motor Neu-ron in the Brain The origin of the firstmotor neuron of the brainis somewhat more compli-cated. Here we must firstdetermine the origin of themotor cerebral nerve, thenuclei of which are identi-cal with the neuron cellsunder consideration, andare similar to
. Diseases of the nervous system . ior horn cells with their dendrites, and of anterior roots which emerge fromthe lateral motor nerve. At the points of cervical and lumbar enlargement the number of neurons ismuch greater, because thereis a larger number of mus-cles to be supplied than isthe case in the thoraciccord. (b) The First Motor Neu-ron in the Brain The origin of the firstmotor neuron of the brainis somewhat more compli-cated. Here we must firstdetermine the origin of themotor cerebral nerve, thenuclei of which are identi-cal with the neuron cellsunder consideration, andare similar to the anterior-horn cells of the spinalcord. I take it for grantedthat the peripheral courseof the nerve fibers is under-stood, and shall refer mere-ly to the fact that the fol-lowing nerves will be con-sidered (Figs. 42 and 43) :The oculomotor nerve (thethird nerve), the trochlear(the pathetic or fourthnerve), the abducens (thesixth nerve), the facial (theseventh nerve), the spinalaccessory (the eleventhThese, as is well known, are. Fig. 42.—Medulla Oblongata, Pons, Peduncles, andAdjacent Parts Seen from the Base. (After Toldt.) nerve), and the hypoglossal (the twelfth nerve). purely motor nerves. In addition are the mixed nerves, the trigeminal (fifth nerve), the glosso-pharyngeal (the ninth nerve), and the pneumogastric (tenth NEURON SYSTEMS AND NEURON DISEASES 51 nerve). We know of the last three that they possess a motor root besidestheir main sensory root. We will now discuss the origin of this first motortract of the cerebral nerves in so far as it has been revealed bv recent inves- tigations. We seek the origin of the oculomotor nerve toward the top of the brain,but still in that portion which we designate the middle brain; here also we
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