When this development and growth of new parts is completed the Nerve System appears as a set of complex organs made of a central axis, brain and spinal cord, and peripheral connections made up of forty-three pairs of directly attached nerves (12 cranial and 31 spinal) with two great gangliated cords and numerous other sympathetic ganglia and communicating cords situated outside the skeletal axis but communicating with it intimately by means of interchange of fibre bundles between the sympathetic and the cerebro-spinal nerves. [Illustration: Schematic diagram of Spinal nerve and Rami. A: Spinal nerve. B: Spinal ganglion. C: Posterior nerve root. D: Anterior nerve root. E: White ramus communicans. F: Gray ramus communicans. G: Sympathetic ganglion. H: Sympathetic cord. After Gray Parker 31. Interchange of fibre bundles between spinal and sympathetic nerves.] But we who have viewed the embryonic development even briefly and sketchily, understand that all these complex organs are merely an aggregation of neurons, each neuron made up of a cell body, one or more axons, and dendrites; that the nerve cells are the controlling elements and the axons the centrifugal carriers of nerve energy, while the dendrites are the centripetal processes through which each nerve cell receives communications. The Body Axis The skull and spinal column, taken together, constitute the bony axis of the body, the center of organization of the skeleton; to these parts are attached other skeletal structures, mandible, ribs and sternum, extremities, classified as the appendicular portion of the skeleton. Likewise are attached, directly or indirectly, the voluntary muscles which move the skeleton, and the vessels and viscera. Any given structure in the body can be traced to a supporting connection with this bony axis. The bony axis contains the neural axis. Its strength and solidity are such as to preserve the integrity of the most vitally important tissue of the body from every form of injury if such protection be possible. Through openings in the bony axis--foramina--the central nerve organs give off or receive the nerve bundles which bring them into communication with every other structure of the body. And the body has been so arranged that every single part of it is partly or wholly under control of nerves emerging through these foramina. Even the brain and spinal cord themselves respond to changes in the blood-vessels which are controlled by nerve impulses which have emerged through the intervertebral or cranial foramina and returned by other routes to supply the muscular coats of the vessels. Concussion of Forces Affects Spinal Column