When, however, we come to inquire into the office of the particular ganglia which exist in Alan and the Vertebrata, it is, in some instances, difficult to determine what object can be gained by a special evolution of nervous force by some of them. It may be inquired what is the func tion performed by the ganglia on the posterior roots of spinal nerves, on the large root of the fifth, on .the glosso-pharyngeal, on the vagus nerves ? Can it have reference, as already suggested in a former part of the article, to ' the part which these nerves perform in connec tion with tactile sensibility or with the sense of , taste, as in the fifth and glosso-pharyngeal, in analogy with the ganglia attached to the olfac tory and optic nerves, and probably with the auditory ? Or have these ganglia anything to do with the nutrition of the parts among which their nerves are distributed, as Dr. Al. Hall suggests, in which case they would present an obvious analogy, and might be classed with the sympathetic ganglia? The data vvhich would assist in coming to a right conclusion upon this subject are so few, that, with our present knowledge, it is impos sible to form anything like a distinct hypothesis regarding it. I would remark with reference to the last-mentioned conjecture that it would receive great support if gelatinous nerve-fibres were found to take their rise from the ganglia and to follow the course of bloodvessels.
With regard to the use of the ganglia of the sympathetic, the proved existence of gelatinous fibres, peculiar to these ganglia and taking their rise from them, distinctly indicates that they are the seat of a special developement of nervous power, whether spontaneously arising in the nutrient changes of ganglia, or "by the reftexion of a change propagated to them by afferent nerves implanted in them. The va rious facts which show that the sympathetic sys tem enjoys an existence and power independent of the cerebro-spinal axis also confirm this view.
But we must enquire further what is gained by the passage of certain nerve-fibres through these ganglia, as is the case with most if not all the tubular fibres connected with them ? It may be that in their passage through the gan glia the tubular fibres acquire an anangeinent in new sets or fascicles in a manner analogous to that which occurs in the plexuses. But this can scarcely be the only object of this connection. Do these fibres associate the cere7 bro-spinal centres with the ganglionic system ? or do they themselves in passing again through vesicular matter experience some modification in their vital endowments ? These questions cannot be satisfactorily solved in the present state of our knowledge.