MINUTE ANATOMY.- The branches of the sympathetic nerve present to the naked eye certain characters which, more or less, dis tinguish them from the proper cerebro-spinal nerves. They have a dull greyish-white ap pearance, different from the white shining aspect which characterises the nerves belong ing to the other class. This appearance is better marked in some parts of the nerve than in others, and is best seen in the branches which accompany the blood-vessels. By Valentin this gray appearance of the sym pathetic nerves was attributed to the presence of the ganglionic corpuscles : this, however, as Remak observed, cannot be the case, inas much as the ganglionic corpuscles are not dis tributed throughout the whole extent of the nerve, but are confined to certain limited parts. Remak believed it to be due to the presence of structures termed by him organic nerve fibres : Volkmann and Bidder also believed it to be owing to a peculiar set of fibres, different, 7-g-F,71 of an inch. They present distinct margins, but have a paler aspect than the above, and do not possess the double contour which is seen in the broader tubular fibres, and many of them often have a tendency to the formation of varicosities. When running in bundles they have, according to Volkmann* and Bidder, who first called attention to their anatomical characters, a yellowish grey hue instead of the white pearly aspect of the cerebro-spinal nerves. Sometimes the two sets of fibres are intermingled and run side by side with each other, at other times they run in bundles more or less distinctly separated. The number of fine fibres which are present much exceeds that of the broader or coarser variety. The two classes of fibres do not, how ever, appear to be distinctly marked off from one another, there being present fibres which possess partly the characters of the one and partly those of the other. When one of the finer variety is examined at the same time with one of the coarser variety, and the two com pared, the points of distinction are sufficiently however, from those of Remak. Whether it
be due to the fibres of Remak or not, it seems to be, at least, best rnarked in those branches of the sympathetic in which these fibres are most abundant. The sympathetic also differs from the cerebro-spinal nerves in consistence as well as in its appearance, being much softer and more readily torn across than the latter. This may be partly due to the want of the strong distinct fibrous sheath possessed by the latter, and partly also to a difference in the character of the nerve fibres themselves. The nerve fibres of the sympathetic are moreover not arranged into distinct fasciculi, but lie together imbedded in a mass of fibrous tissue which accompanies them, serving the purpose of a sheath.
As regards the constituents of the sympa thetic nervous trunk, when a portion of one of the main cords is examined with a power of 250 diameters, it is found to be composed of the following elements: 1st. Tubular nerve fibres ; 2nd. Structures which present a homo geneous flattened appearance, and contain a number of oval nuclei imbedded in them at intervals ; and, 3rd. a quantity of white fibrous tissue.
The tubular nerve fibres which are present in the sympathetic, differ much in point of breadth from one another. Some of them measure about „,„. to 1-1-6-6- of an inch in diameter : their contents present the arrange ment of double contour and axis cylinder which characterise the fibres occurring in the eerebro-spinal nerves. Besides these fibres there are others present which have also the character of the tubular fibre, but are much finer, measuring only from the to the marked, but a gradual transition from the fibres belonging to the one set to those belonging to the other may, in some parts of the sympa thetic, generally be traced. The finer the nerve tubules are, the less distinctly do their contents appear to be separated into central portion or axis cylinder, and white substance of Schwann.