[Illustration: FIG. 6. A cell of another form, from the superficial or outer part of the greater brain (cortex cerebri). The great amount of branching is suggestive of the power to receive and to transmit nervous influences (impulses) from various other cells; in other words, complexity of structure suggests a corresponding complexity of function.] [Illustration: FIG. 7. Representation of the manner in which a nerve is seen to terminate in a muscle, such ending being one form of "nerve-ending" termed a "muscle plate." It tends to emphasize the close relationship existing between muscle and nerve, and to justify the expression "neuro-muscular mechanism," the nervous system being as important for movements as the muscles. (Schaefer's _Histology_.)] [Illustration: FIG. 8. Three muscle-fibres lying beside each other, with the small blood-vessels (capillaries) around and between them. Such are the appearances presented under the microscope by skeletal or striped muscles such as those of the larynx. (Schaefer.)] It may be said, in general terms, that the nervous _centres_, the brain and the spinal cord, which are parts of one anatomical whole, are characterized by the presence of the cell-bodies as well as their extensions, while nerves consist only of the extensions or arms of the cell-bodies. The nerve-cell whose body is in the top of the brain may have an extension or arm which may reach practically to the end of the spinal cord, and there make communication with another cell whose arm, in turn, may reach as far as the toe. Such nerve arms or extensions constitute the _nerve-fibres_, and bundles of these _nerves_, or _nerve-trunks_.