In the Vertebrata the axis is dorsal, and is called the _cerebro-spinal axis_, including brain and spinal cord. When we look at this structure superficially we see various nerves radiating _from_ it to skin, glands, and muscles; but a closer examination, enlightened by knowledge of function, shows that some of these nerves pass _into_ it from the various surfaces and sense-organs, and are therefore called _afferent_ or _sensory_; whereas another set passes out of it to glands and muscles, and these nerves are therefore called _efferent_ or _motory_. There are also fibres which, passing from one part of the great centre to another, are called _commissural_. To this brief account of the cerebro-spinal system may be added a word on the connected chain of ganglia and nerves known as the Sympathetic, because it was formerly supposed to be the organ through which the various “sympathies” were effected. It is now held to be the system devoted to the viscera and blood-vessels; but there is still great want of agreement among physiologists as to whether it is an independent system, having a special structure somewhat different from that of the cerebro-spinal, or whether it is simply a great plexus of nerves and ganglia, only topographically distinguishable from the rest of the nervous system. Into this point it is unnecessary for me to enter here. Enough to say, that I entirely agree with Sigmund Mayer in adopting the second view.[80] In no histological character, yet specified, are the sympathetic nerves and ganglia demarcated from the others. There are, indeed, _more_ non-medullary fibres (the gray fibres of Remak) in the sympathetic; but the same fibres are also abundant in the cerebro-spinal system; and the sympathetic has also its large medullary fibres.