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It has even been supposed that in diluvial deposits the presence of 'dendrites' might be regarded as affording a certain mark of distinction between bones mixed with the diluvium at a somewhat later period and the true diluvial relics, to which alone it was supposed that these deposits were confined.
It consists of a rounded mass of protoplasm, containing a well-defined nucleus. 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.
Moreover, the anatomical evidence of such changes taking place is at present of the flimsiest character. If these theories be true, what, it may be asked, is the agency that causes the dendrites to contract or the neuroglia cells to expand? Is there really a soul sitting aloof in the pineal gland, as Descartes held?
It is held possible that the dendrites or branching processes of nerve cells are contractile, and that they, by pulling themselves apart, break the association pathways which are formed by the interlacing or synapses of the dendrites in the brain.
The surface of all the bones is in many spots covered with minute black specks, which, more especially under a lens, are seen to be formed of very delicate 'dendrites'. These deposits, which were first observed on the bones by Dr. Meyer, are most distinct on the inner surface of the cranial bones.
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.
But it serves as a stimulus for the neuron with which the first connects and starts an impulse in this connecting neuron, the point of stimulation being where the fiber terminations of the first neuron make connection with the dendrites of the second. This impulse in turn stimulates the next neuron, and so on, producing a series of impulses along a given nerve path.
Its summit was flat, rough, and rocky; at the distance of four miles from our camp it receded a little from the river, and there limestone was observed, crowded with fossils like that on the opposite side of the river. Two miles farther, the bed of the river was formed by a felspathic rock, with beautiful dendrites.
Occasionally their antiquity is indicated not only by their colour but by superficial incrustations of carbonate of lime, or by dendrites formed of oxide of iron and manganese. The edges also of most of them are worn, sometimes by having been used as tools, or sometimes by having been rolled in the old river's bed.
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.
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