506 Brown-Sequard, instituted for a different purpose, that the I sensory and motor roots that are OM-a-ws in the spinal cord are continuous channels for this kind of interchange.* It is highly probable therefore that such a relationship between individual muscles does exist. It has further to be remarked, in corroboration of the interpretation here offered, that the tendency to alternate the limbs is noticeable among the earliest movements of the child, and is generally believed, as an

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... ive action, to depend upon some primitive arrangement of the system. Nor is it to be forgotten that, corresponding to the superiority of man over all other animals in respect to the regularity and ease of his gait, we have the remarkable fact that the decussation in the spinal cord is found more complete in him than in any other known instance. Man was made to walk, and is incontestably the paragon at that exercisea circumstance which, notwithstanding its advantages, a little frustrates his attempts at other modes of progression. When ever the to-and-fro excitation is not available, the movement is laborious. This is particularly the case when, instead of the alternate, the consentaneous action of the two sides of the body is employed, as in swimming. The exhaustion which so speedily supervenes in movement in the water is, no doubt, greatly owing to the loss at each stroke of the volitional stimulus which is so admirably husbanded in walking. The action is similar to leaping, where a pause is required _per saltum, not merely for the purpose of renewing the effort, but, as it would seem, to allow the muscles to discharge their stimulus, the benefit of which is thus completely lost. Although no attempt has been made in the course of these