THE RELATION BETWEEN THE OCCURRENCE OF WHITE RAMI FIBERS AND THE SPINAL ACCESSORY NERVE. By A. H. ROTH, A. B., M.D., Instructor of Anatomy in the University of Michigan. With One Figure. In two important papers published in 1886 and 1889 GASKELL pointed out that the spinal accessory nerve in the dog contained in its upper part fine calibered fibers resembling those which formed the visceral efferent fibers of the thoracic nerves, and concluded that these fibers represented the white rami communicantes of the upper cervical nerves. Furthermore he revived, in a new form, the view propounded long before by BELL, in supposing that instead of but two roots, each segmental nerve of the body possessed in addition visceral roots, which, so far as their efferent fibers were concerned, were associated with a lateral column of cells in the central nervous system. Throughout a considerable portion of the spinal region these visceral efferent fibers form the white rami communicantes; in the cranial region they are represented by those fibers which, since the embryological studies of His demonstrated so clearly their distinctness, are generally known as the lateral motor roots. And since the fibers of the lower roots of the spinal accessory belong to the lateral motor series, and according to GASKELL'S view the upper roots represent white rami communicantes, there follows the conclusion that a correlation should obtain between the spinal accessory nerve and the occurrence of white rami passing from the spinal nerves to the sympathetic cord. In the dog GASKELL found in the anterior roots of the spinal nerves from the 10th to the 25th, large numbers of very fine calibered medullated fibers, their diameter varying from 1.8 to 2.7 with a few reaching 3.6 μ. He found also that the tenth nerve, i.e., the second thoracic, in which these fibers first appeared, was the uppermost one which had a white ramus communicans connected with it and furthermore he found that this white ramus was composed almost entirely, so far as its medullated fibers were concerned, of fibers of a similar calibre to those first occurring in the anterior root of the tenth nerve. The conclusion naturally followed that the fine calibered fibers of the anterior roots were the white rami fibers and that the first group of such fibers given off from an anterior spinal root was that of the second thoracic. If these conclusions be correct, then it is clear that in the dog there is a distinct gap between the first nerve which possesses a white ramus and the level at which the lowest root of the spinal accessory nerve arises, this root being given off at about the level of the seventh cervical nerve, three segments above the level of the first white ramus. Such a condition does not accord with GASKELL'S view as to the significance of the spinal accessory and it seemed that it might be of interest to investigate the relations of the two structures, spinal accessory and white rami, in other mammals with a view to ascertaining whether the discord was of general occurrence or whether some correlation really existed. For this purpose it seemed advisable to select first of all some form in which the origin of the lowest root of the spinal portion of the spinal accessory occurred at a decidedly different level than in the dog. BISCHOFF (1832) in his comparative study of the spinal accessory found that in mammals there was a considerable difference in the distance to which the nerve descended into the cervical region. Thus, he found that it descended in the weasel to about the level of the second cervical nerve; in the mole, rat and marmot to that of the third cervical; in the rabbit to that of the fifth cervical; in the stonemarten, stag, cat, wolf and man to that of the sixth cervical; and in the pig, dog, and calf to that of the seventh cervical. Having regard to these data the rat was chosen as a suitable form for study, especially as it was one readily obtained; and a study of the distribution of small medullated fibers in the anterior roots of the cervical spinal nerves and in the rami communicantes with reference to the lowest root of the spinal accessory was made in that form. Some observations were also made upon the cat and dog, but rats fully grown, formed the principal object of study. Before proceeding to consider the conditions in the rat it is necessary to define what is meant by a white ramus fiber. GASKELL limited the term to small fibers which were distinctly grouped in bundles, and on this basis made a special point of the occurrence of the uppermost white ramus communicans in connection with the second thoracic nerve. But is such a limitation justifiable?, Must it be supposed that fibers of the same quality are always grouped together in distinct bundles? Such does not seem to be the case throughout the central system and from what is known as to the association in bundles of fibers of very different origin in both the central and peripheral systems -e. g. the so-called mesial fillet fibers with the fillet in the central system, and the chorda tympani with the lingualis fibers in the peripheral system-it would seem that the mode of grouping of fibers so far as their quality or origin is concerned, is, to some extent at least, fortuitous. It seems quite possible that when but a relatively small number of white rami fibers exist, they may not form a distinct bundle, but may be incorporated in a single trunk with grey rami fibers and may, if their number be very small, be scattered among such fibers. In other words, it is possible that the ordinary use of the terms white and grey ramus is merely relative, indicating merely the preponderance in the nerve trunk of one or the other variety of fibers. The observations of HARMAN (1900) on the occurrence of white rami fibers in man makes this possibility very prominent and my observations upon the rami communicantes of the lower cervical and upper thoracic nerves of a dog are also of interest in this connection. In sections of the ramus connected with the 6th cervical nerve four distinct bundles were found. Three of these were quite small, while the fourth was large, its area exceeding considerably that of the other three combined. The three small DESCRIPTION OF FIGURE. Transverse sections of the rami communicantes of the sixth cervical to the second thoracic nerves in the dog. The outlines were traced with a camera lucida; the shaded areas represent white fibers and the unshaded grey, but no attempt has been made to represent the actual number of white fibers in the rami in which they are abundant, the eighth cervical nerve, for example, containing more white rami than the sixth in which they are interspersed with grey fibers. bundles were wholly composed of non-medullated fibers, but the large one, though mainly non-medullated, contained imbedded in its central portion a large number, at least 250, small calibered medullated fibers. On superficial inspection, such a ramus would undoubtedly appear to be a gray ramus since the white fibers were almost entirely invested by the non-medullated ones. The ramus of the seventh cervical nerve consisted of three bundles, two of which were entirely grey, while the third contained a few, about 25, medullated fibers. The eighth ramus consisted again of three bundles, one of which was large and grey, containing only about half a dozen small medullated fibers, the second small and almost entirely grey, while the third was almost entirely composed of white fibers, although two small groups of grey fibers occurred at its periphery. These two small bundles were fused in the upper part of the ramus. The first thoracic ramus consisted of five bundles, one of which was exceedingly small, consisting of not more than about one dozen fibers, six of which were medullated. Of the other bundles two were almost entirely grey, containing each from ten to twelve medullated fibers, while the other two were mainly white, one entirely so, the other however containing a considerable number of grey fibers. Finally in the second thoracic ramus four bundles were present, two of which were almost entirely grey, containing each only a half dozen small white fibers, while the other two were entirely white. In connection with the second thoracic there are two bundles which may properly be designated white rami, in connection with the first thoracic one, and in connection with the three lower cervical none. But in each of the cervical rami and in an additional bundle of the first thoracic small white fibers exist which are in no wise different either in appearance or size from fibers composing recognized white rami. Only by determining the origin and termination of these fibers can it be definitely decided that they are really white rami fibers, but if there is anything to be concluded from their size and their similarity to the fibers of the white rami, then they are undoubtedly of the same nature as these latter, and they will be termed white rami fibers in what follows. Evidence as to the nature of the fibers may be derived from physiological experimentation. The observations of NAWROCKI and PRZYBYLSKI (1891) and more especially of LANGLEY (1892) certainly do not favor the view that the fibers in question are white rami fibers, since they found that in the cat, in which the conditions are very similar to those obtaining in the dog, no dilatation of the pupil resulted from stimulation of the anterior roots of nerves above the eighth cervical, LANGLEY |