The Adult Nerve System
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.
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.