" The nerves distributed to this apparatus come exclusively from the fifth pair, and more particularly from the branchesspringing from the anterior portion of the root. l.:ach follicle (fig. 486) is of a spheroidal form, slightly compressed on the side which adheres to the neighbouring fol licle, and its diameter is about ilith of an inch. I have found these dimensions the same in ani mals of very different size. These follicles are. never free or floating in the gelatinous fluid so abundant in these fishes : on the contrary, they are always firmly fixed, as if with a special view I to their security, for they are planted on un yielding aponeurotic expansions, like that of the muzzle, or else on fibrous bands extending along the fin, and having no other use. When the gelatinous fluid which envelopes these folli des is examined under the microscope, it is seen to contain numerous fibres passing in va rious directions, and fixed to the surface of the follicles.
" Each follicle is formed of two membranes (f and g) which adhere together on the side towards the fibrous band which supports the organ, whilst on the opposite side they are sepamted by about a third of the vertical diameter of the follicle. These organs may be easily examined by a very slight magnifying. power, it being only necessary in the first place' to remove the investing gelatinous substance,' and then to subject them to moderate compres- I sion for the display of their interior. In a follicle thus compressed, we observe first the cut portion of the tendinous band cc, then thel outer membrane enclosing the other, in which is the rounded granular mass e already men- , trolled. This latter seems to rest upon the lower wall of the internal membrane. The ex ternal membrane adheres by its lower border to the fibrous band beneath it in such a way, that between this external wall of the follicle and the internal is left a space, in which the nervous ramification d advances and adheres to the rounded mass of granular substance.
" In the follicles of the longitudinal series of the fin, of which we here speak, the nervous twig is derived from the fifth pair and passes first through a slit in the tendinous band. After passing this aperture it bends. underneath the granular mass, and again emerges at the base of the follicle, but at the opposite side from that at which it entered. It is remarkable that the nerve is much thinner at its exit, and re duced to an exceedingly delicate filament (/), which proceeds along, the tendinous band to the next follicle, penetrating its wall and join ing its nerve at the point of its flexion under the granular mass (k).
" On examining under the microscope the rounded granular mass, made flat by the com pressor, and after the removal of the membranes of the follicle, we see the nerve running length wise over it from end to end, the anastomosing branch coming from the preceding follicle (k) and tbe very delicate filament which proceeds to that next in order (/). We further remark that the nerve of the follicle, in its course along the granular mass, gives off a great number of elementary fibres, which disseminate themselves through the mass and thus reduce the nerve to so small a size. Sometimes I have fancied that
these fibres formed lOops and returned ; but I have never obtained a clear view of their termi nation. I am no less doubtful regarding the course of the elementary fibres of the anasto mosing branch coming from the preceding follicle. Sometimes I have seen these fibres return towards the slit in the tendinous band and rejoin the nerve in order to regain the centre. In other cases I have seen these fibres pursue their primitive direction, and .pass on with the rest towards the opposite end of the granular mass. Hence I imagine that the fibres of the anastomosing, bundle do not all follow the same course, and that while some advance into the granular uaass, others turn back towards the centre through the slit in the fibrous band." " It occasionally happens that two nervous twigs pass from the main branch to the same follicle. When this happens, there are always two distinct granular masses." M. Savi then describes accurately the arrangement of the several series of these follicles in the torpedos which he examined, an account of which is not necessary for our present purpose. In one example he found that the follicles amounted in all to two hundred and fourteen.
We cannot adduce these remarkable and peculiar structures as at present throwing any light on the function of the Pacinian corpuscles, since we must confess with M. Savi that as yet we are entirely ignorant both of their real nature and use. Nevertheless the resemblance is such as, it is hoped, will warrant the introduction of the preceding account, which is new in this country, and very interesting in itself. It is unnecessary to recapitulate the several points of similarity and difference, which, after the de tailed description of each now offered, may be readily apprehended by the reader himself.
It only remains that we should direct atten tion to the very admirable memoir of Henle and Kolliker on this subject. They corrobo rated the principal results of Pacini, and added many most valuable observations which the use of higher powers of the microscope and perhaps greater experience in research had enabled them to make. These observations M. Pacini has recently informed me he has himself almost entirely confirmed. An excellent abstract of their labours appeared in the British and Foreign Medical Review for January, 1845, and in the following April Dr. Todd and myself gave an account of these structures, drawn up from origi-. nal observations and containing some new results, though on the whole confirmatory of those previously published. See the PHYSIOLOGICAL ANATOMY AND PHYS/OLOGY OF MAN, VOI. p. 395.
It is right to add that MM. A. G. Andra], Camus, and Lacroix, met with these bodies in 1833, and that they were noticed subsequently by Cruveilliier and Blandin in their respective works on descriptive anatomy, bnt without any real light being thrown on their nature or internal structure.
( William Bowman.)