Animal life resides in the nervous system alone, and its character is proportioned to the development thereof, of which the brain is the principal mass. A subordinate portion of the general life, however, is in the nervous system of the body, and in proportion as the brain declines in development the relative amount of psychic energy in the body is greater. Thus the body of the alligator after decapitation is capable of sensation and voluntary acts, such as pushing away an offending body with its foot. The character of the life in the body is explained by physiology and sarcognomy. Its universal presence is due to the universal diffusion of the nervous system, of which the accompanying figure, showing the location of the spinal cord and spinal nerves, will give a proper conception. In this figure the spinal cord, with its thirty pairs of nerves, eight cervical at the neck, twelve dorsal in the back, five lumbar in the loins, and five or six in the sacrum (between the hips), is seen descending from the base of the brain below the cerebellum (which is rather too large in engraving), and proceeding throughout the body until lost in fine ramifications which the microscope can scarcely trace, but which quickly inform us if they are touched or disturbed. [Illustration] It cannot properly be said that the spinal cord proceeds from the brain, nor on the other hand that the brain proceeds from the spinal cord, for they originate simultaneously in a soft, jelly-like condition in which the microscope cannot detect the latent structure, not as they are in the adult, but as they are in the foetus in which they first appear, with a structure similar to that of the lowest class of vertebrate animals, the fishes. From this embryonic condition, in which there is very little resemblance to the adult brain, its progress has been carefully traced by many observers, but chiefly by Tiedemann, through all the stages of life before birth into the soft, infantile form of the human brain. Some knowledge of this embryonic growth is necessary to a correct understanding of the adult brain, its essential plan, its growth, and the correct estimate of its development.