tin, travel round the margin of the ganglion, and to these he gives the name of untspinnende Fasern, surrounding fibres, and some fibres pass from them to the more central ones, or from the latter to the former. Nerve-vesicles exist at the circumference of the ganglion as well as in its interior, and to them is due the peculiar grey colour of that body.
The best mode of examining these points is to select the smallest ganglia of very small animals, birds, inice, &r.c.; these, when sub jected to compression, become very transpa rent, and display much of their intrinsic ar rangement. Or thin slices of large ganglia may be placed under the microscope, and when torn up by needles the disposition of the nerve vesicles and the caudate processes, when pre sent, are rendered visible. And none is more suitable for this purpose than the Casserian ganglion of the fifth nerve, which by the ab sence of a dense sheath and its greater loose ness of texture is more easily examined.
It is a highly important problem, in minute There does not appear to be any material difference of structure between the ganglions of the sympathetic and those of the cerebro-spinal system, excepting, as lienle states, the exist ence of a greater number of gelatinous fibres in the former.
Of the cerebro-spinal centre.—The nervous mass which occupies the cavities of the cra niutn and spine doubtless constitutes one great centre, as there is a perfect continuity through out all its parts. But the differences of external form and characters in some regions of it, and the obvious diversity of endowment of the nerves connected with certain portions, denote and justify an anatomical as well as a physiological subdivision of it into segments, each of which is a centre of nervous action independent of the rest, yet so connected with them that the func tions of all are made to harmonize in the most perfect manner.
The subdivision which the external anatomy indicates, although not perfectly coincident with that which the differences of function would suggest, has been so long sanctioned by usage and is so convenient for description, that no advantage would be gained by adopting any other. Our description of the cerebro-spinal centre, or axis as it has also been called, will be given under the following heads : I. the spinal cord; 2. the encephalon, including a, the medulla oblongata; b, the mesocephale; c, the cerebellum; d, the cerebrum.