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The nerve is seen to be a bundle of axons, or nerve fibers, held together by connective tissue, while the ganglion is little more than a cluster of cell-bodies. *End-to-end Connections.*—These consist of loose end-to-end unions of the fiber branches of certain neurons with the dendrites of other neurons.
If Axon happened to be a subject of a conversation and there was any uncertainty as to which Axon out of a thousand Axons he might be, the introducer of the subject would always say, "You know sandy-haired fellow." This described him hair, beard, moustache. Sandy-haired men have no age until they are fifty-five, and Axon was not fifty-five.
Tracts of association are probably formed in definite lines through the nervous system, as during the life of a child repeated waves of sense impulses beat against and overcome resistances, and make smooth pathways here and there through the brain structure. Thus may be produced growth of axons in certain directions, and synapses of this cell with that.
It is divided into three lobes—a central lobe and two lateral lobes—and weighs about two and one half ounces. In its general form and appearance, as well as in the arrangement of its cell-bodies and axons, the cerebellum resembles the cerebrum.
*Side-by-side Connections.*—On separating the ganglia and nerves into their finest divisions, it is found that the nerves consist of axons, while the ganglia are made up mainly of cell-bodies and dendrites. But the axons, in order to connect with the cell-bodies, must terminate within the ganglion, so that they too form a part of it.
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.
Certain of the axons have no primitive sheath and others are without a medullary sheath. *Form and Length of Axons.*—Where the axons terminate they usually separate into a number of small divisions, thereby increasing the number of their connections. These collateral branches, by distributing themselves in a manner similar to the main fiber, greatly extend the influence of a single neuron.
In the matter of length, great variation is found among the axons in different parts of the body. In certain parts of the brain, for example, are fibers not more than one one-hundredth of an inch in length, while the axons that pass all the way from the spinal cord to the toes have a length of more than three feet. Between these extremes practically all variations in length are found.
The cortex is greatly increased in area by the presence everywhere of ridge-like convolutions, between which are deep but narrow depressions, called fissures. The interior of the cerebrum consists mainly of nerve fibers, or axons, which give it a whitish appearance. The cerebrum is a double organ, consisting of two similar divisions, called the cerebral hemispheres.
When a man like Lord Brougham can at any moment shut himself away from the outer world and fall asleep, does his soul break the dendritic contacts between cell and cell; and when he awakes, does it make contacts and switch the impulses evoked by sense stimuli on to one or other tract of the axons, or axis cylinder processes, which form the association pathways?
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