STRUCTURAL PLAN OF THE HUMAN BRAIN. 375 



of the nerve fibers are of the Golgi type — that is to say, they end 

 as well as begin within the central nervous system. The bundle 

 of nerve fibers which pass out together constitute a nerve, or, to 

 speak more correctly, a nerve root. So far as yet observed no ex- 

 ception occurs ; therefore we may safely assert that every nerve- 

 cell of the brain or spinal cord produces one nerve fiber and only 

 one, and this fiber grows out from the nervous system into the 

 tissues of the body. The fiber is single at its origin, but since we 

 always find the peripheral fibers branching, we may add that the 

 fiber is multiple at its termination. The nerve cells acquire also 

 other secondary branches — the so-called protoplasmatic processes 

 or dendrites — which grow out from the cells, but are not nerve 

 fibers and are confined in their growth to the nervous tissue itself. 

 The secondary branches present highly characteristic variations in 

 the different regions of the brain, as described in the text-books. 



By the ganglionic portion we now understand the nerve cells 

 which lie in little groups outside of the medullary tube. These 

 cells produce fibers, which grow in two directions — on the one 

 side into the brain or spinal cord, on the other away from the 

 brain and cord into other tissues and organs. It has been ob- 

 served that the ganglionic nerve cells elongate and become spin- 

 dle-shaped ; each pointed end of the cell grows out into a nerve 

 fiber ; as the nerve cell connects the two fibers, we may describe 

 the actual condition accurately as resulting in a single nerve fiber, 

 which has a nerve cell interpolated in its course. Each group of 

 nerve cells forms a bundle of nerve fibers, which constitute the 

 posterior (or so-called dorsal or sensory) root of the anatomists. 

 If we follow a ganglionic fiber into the spinal cord or brain, we 

 find that it forms two branches, as first recorded by Ramon y 

 Cajal, a distinguished Spanish histologist ; of these two branches, 

 one runs upward, or in the brain forward, and the other runs 

 downward, or in the brain backward ; each fork gives off second- 

 ary branches (collaterals), that ramify still further, and are all 

 situated within the central nervous system proper. If we study 

 the termination of the ganglionic fiber at its other end — that is to 

 say, in the tissues or organs — we find that there also there occur 

 several ramifications. These fibers, like the medullary fibers, have 

 each a single origin, but, unlike the medullary fibers, have two 

 sets of multiple terminations. Although both the peripheral and 

 central terminations have been carefully studied, they have never 

 been found connected with other structures or cells, but only to 

 be in contact with them. 



The true history of the ganglia and their nerve fibers has been 

 elucidated chiefly through the masterly researches of Wilhelm 

 His, Professor of Anatomy at Leipsic, who is the recognized high- 

 est living authority on the development of man. This addition 



