The cerebrum, or brain proper, occupies the anterior portion of the cranial cavity. It is ovoid in shape, with an irregular, flattened base, and consists of lateral halves or hemispheres. The greater part of the cerebrum is composed of white matter. The hemispheres of the cerebrum are usually said to be the seat of all psychical activities. Only when they are intact are the process of feeling, thinking, and willing possible. After they are destroyed the organism comes to be like a complicated machine, and its activity is only the expression of the internal and external stimuli which act upon it. The spinal cord, or spinal marrow, is that part of the cerebrospinal system which is contained in the spinal canal of the backbone, and extends from the medulla oblongata to a short distance behind the loins. It is an irregularly cylindrical structure, divided into two lateral, symmetrical halves by fissures. The spinal cord terminates posteriorly in a pointed extremity, which is continued by a mass of nerve trunks--cauda equinae. A transverse section of the cord reveals that it is composed of white matter externally and of gray matter internally. The spinal cord does not fill the whole spinal canal. The latter contains, besides, a large venous sinus, fatty matter, the membranes of the cord, and the cerebrospinal fluid. The spinal nerves, forty-two or forty-three in number, arise each by two roots, a superior or sensory, and an inferior or motor. The nerves originating from the brain are twenty-four in number, and arranged in pairs, which are named first, second, third, etc., counting from before backward. They also receive special names, according to their functions or the parts to which they are distributed, viz: 1. Olfactory. 2. Optic. 3. Oculo-motor. 4. Pathetic. 5. Trifacial. 6. Abducens. 7. Facial. 8. Auditory. 9. Glossopharyngeal. 10. Pneumogastric. 11. Spinal accessory. 12. Hypoglossal. Inflammation of the Brain and its Membranes (Encephalitis, Meningitis, Cerebritis).