cells, when the nerve-tubes come off' at either extremity, as they generally do, while one of When both nerve-tubes pass off; not at op posite extremities, but from one side of the corpuscle, they both run, according to Bidder, in the direction of the periphery. As regards the mode of connection between the ganglionic corpuscle and nerve-tube, the cell-wall of the former appears to be directly continuous with the membrane of the latter, while the contents of the vesicle seem to be prolonged down wards into the nerve-tube, becoming continuous with its contents. The nucleated substance forming the capsule of the ganglionic corpuscle is also, according to Kiilliker, prolonged along the nerve-tube which arises from the corpuscle itself (fig. 288. and 289.). All the nerve-tubes which are thus connected with the ganglionic corpuscles in the ganglia of the sympathetic belong to the finer variety of tubular fibres already described. In the spinal ganglia, according to Kolliker, the nerve-tube.s arising from the corpuscles are at first fine, mea suring about 0'0015-0'0025 of a line ; but in their further course many of them increase in diameter up to 0.003-0.00-1 of a line, or even to 0'005-0-006 of a line, so as to represent broad nerve-fibres, or fibres intermediate be tween the broader and finer varieties.
Most of the cells which are seen in ex amining the ganglia of the mammalia belong either to the apolar or bipolar variety. It is pos sible, however, that many of them, as Wagner, Robin, &c. maintain, although apparently apo lar, are really unipolar or bipolar cells, from which one or both processes have broken off during the process of preparing them for ex amination. That the bipolar cell exists in with the walls of the included ganglionic puscle, and appears to hold much the same man and other mammalia, is proved by the observations of Schrceder van der Kolk in regard to the cervical ganglia of rnan, as men tioned by Donders and Harting. Schaffner also describes a bipolar cell in the ganglion Gasseri of the sheep ; and similar cells have been observed by Corti* and Pappenheim in the acoustic nerve of the pig, and by Frey in the Gasserian ganglion of the cat. In the common trunk of the pneumogastric and sympathetic nerves in the middle of the neck, in the young calf, oval cells may be seen which have distinctly attached at their peripherical extremity a nerve-fibre ; and some of them also appear to be connected with one at the opposite or central extremity.
The different cells composing a ganglion are each surrounded by a more or less clear, homo geneous substance, in which are contained a number of round or oval nuclei. These are seen to form a single or double row around the margin of the ganglionic vesicle, their long axis being directed in the axis of the cir cumference of the cell (fig. 288.). They are also seen upon the surface of the corpuscle (e, Jig. 288.). This substance not unfrequently presents a more or less fibrous aspect, as if composed of spindle-shaped corpuscles. It re sembles much (as has been already stated) the fibres of Remak. The nuclei measure from the
to the 4 010 th of an inch in breadth, and about 40100th to -„-1,)--,th of an inch in length. The structure in question is closely connected relation to it that the fibres of Remak hold to the nerve-tubes. It has been termed the capsule of the ganglionic corpuscle. The cap sules snrrounding the different ganglionic cor puscles are also closely united to each other, so as to form a kind of framework, in the loeuli of which the ganglionic corpuscles are placed (fig.288.). It would appear also to be prolonged along the nerve-tubes connected with the gam. glionic corpuscles for some distance, forming for them an investment or sheath similar to that which it forms for the corpuscles them selves. The quantity of this substance which is present varies in different circumstances. It appears to be more abundant in some cases than in others, and is commonly more so in the sympathetic ganglia than in those on the posterior roots of the spinal nerves.
As regards the arrangement of' the nerve fibres in the ganglia, when one of the. enter ing branches in the ganglia of small animals, such as the mouse, is traced into the point at which it joins the ganglion, it is found to spread out somewhat, and soon breaks up into its component fibres. These separate from one another, running amongst the gan glionic corpuscles, either singly or in bundles of two, three, or more. The nerve-fibres be longing to one bundle leave it and join neigh bouring bundles, so that a more or less com plete interchange of the fibres contained in the different bundles takes place; and at the same time there is formed a sort of plexus or network, in the meshes of which the ganglionic corpuscles are imbedded (fig. 287.). Some times, as Valentin observed, one or more of the fibres of one of the entering bundles are seen to wind round the ganglionic corpuscles, and appear again to pass into another entering bundle, thus pursuing apparently a retrograde course. The fibres which thus surround the ganglionic vesicles were termed by Valentin umspinnende fasern ; whether they again really leave the ganglion in the direction in which they entered it, and in this way may he regarded as terminating in a looped arrange ment in the ganglion, it is difficult to deter mine.Hiker* has observed that the nerve tube arising from a ganglionic corpuscle fre quently makes one or two turns around it before pursuing its course towards the peri phery ; and it appears probable therefore that many of the so-called unispinnende fasern may be of this description. That the nerve-fibres connected with the ganglia do not merely pass through it between the ganglionic corpuscles, as was formerly supposed, but enter into intimate organic connection with these bodies, either arising from them, or having these bodies developed upon them in their course from the centre towards the periphery, as seems to be the case with most of the bipolar cells, is quite certain.