The protoplasm is similar to that of other cells,
but is characterized by the presence of many small granules and has a
slightly grayish color.
The _dendrites_ are short extensions from the cell-body. They branch
somewhat as the roots of a tree and form in many instances a complex
network of tiny rootlets. Their protoplasm, like that of the cell-body, is
more or less granular. The dendrites increase greatly the surface of the
cell-body, to which they are related in function.
The _axon_, or nerve fiber, is a long, slender extension from the
cell-body, which connects with some organ or tissue. It was at one time
described as a distinct nervous element, but later study has shown it to
be an outgrowth from the cell-body. The mon-axonic neurons are so called
from their having but a single axon.
*Di-axonic Neurons.*--Neurons belonging to this class have each a
well-defined cell-body and two axons, but no parts just like the dendrites
of mon-axonic neurons. The cell-body is smooth and rounded, and its axons
extend from it in opposite directions (Fig. 127).
[Fig. 127]
Fig. 127--*Diagram of a di-axonic neuron.* The diagram shows only the
conducting portion of the axon, or axis cylinder.
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