22 ANATOMY OP THE CENTRAL NEETOUS SYSTEM. 



ing it or surrounding it with its terminal ramification {Endpinselung). If 

 the cell-body is not very large, it has, nevertheless, abundant points of con- 

 tact through its numerous dendrites; but, if it is very extended, as in the 

 cells of the spinal ganglia, the dendrites are less needed. 



The dendritic processes break up into a more or less abundant branch- 

 ing, whose surface may be further increased by the presence of innumerable, 

 small, pedunculated knots (Fig. 152, I). A transformation of dendritic 

 fibers into peripheral (efferent) nerves has not been demonstrated.^ 



On the physiological significance of the dendrites there are great difEer- 

 ences of opinion. According to the author's investigations and from what 

 may be learned from figures contributed by others, it seems most probable 

 that the dendrites represent an increase of surface of the ganglion-cell, which 

 is absolutely necessary to insure intimate relations with the surrounding 

 fibers of neuraxons (from other cells). In Fig. 16 may be seen (a) the 

 terminal process of a sensory cell of the olfactory epithelium passing as an 

 olfactory nerve, or fila olfactoria, through the cribriform plate and breaking 

 up into terminal fibrillse in the olfactory lobe of the brain (see also Fig. 94). 

 Their terminal ramifications intimately embrace the dense dendritic fibers 

 from the ganglion-cells there located. Here one sees the relation between 

 the olfactory tract of the first order and those cells from which are developed 

 the olfactory tract of the second order, whose course lies within the olfactory 

 lobe. The connection is here established only through the relation which 

 the neuraxon of one cell bears to the dendrites of another. 



Dendrites and neuraxons do not always pass off from the cell-body at 

 difEerent places. Among the vertebrates one may often notice that the 

 cell sends out a process, that appears quite like a dendritic process, from 

 near the origin of which a neuraxon branches off. Among many inverte- 

 brates this is, indeed, the rule. In the river cray-fish, for example, the pear- 

 shaped ganglion-cells send out usually one thick branch from which the 

 dendrites branch off laterally and the neuraxon develops farther on (Fig. 8). 

 Here appears to be a condition which indicates that the two kinds of proc- 



^ The most recent writings of American neurologists show a practical unanimity 

 in the use of the term dendrite for the afferent cell-processes, and Neuraxon, Axone, 

 or f\eurite for the efferent cell-processes. In a vast majority of cases the dendrites 

 are short, protoplasmic processes structurally, while the neuraxon is a long nerve- 

 fiber having the structure described usually as an axis-cylinder. Figs. 15 and 16 make 

 it evident that the afferent sensory nerve-fibers are dynamically to be classified with 

 the dendrites; moreover, their development indicates a similar thing. These afferent 

 sensory nerves are structurally axis-cylinders. In order to avoid ambiguity and con- 

 fusion in this translation, the term neuraxon will be uniformly used for the efferent 

 cell-processes. If the term axis-cylinder is used it will be understood to apply strictly 

 to the structure of the fiber. — W. S. H. 



