hardened in osmic acid and sections cut, they are seen to have the characters of white rami; that is, they consist chiefly of small medullated fibers collected in bundles, with a few medium. or medium sized fibers; between the bundles are a variable number of non-medullated fibers; besides these there one or more grey rami, i.e., bundles consisting chiefly of non-medullated fibers, but containing scattered medullated fibers." These results are entirely in harmony with the author's experimental observations and show a marked discrepancy between the occurrence of efferent white rami fibers and the development of the spinal accessory. In four out of five cats examined in connection with the present study, the level of the lowest root of the spinal accessory agreed with that assigned to it by BISCHOFF, that is to say, it occurred at the level of the sixth cervical nerve. In the fifth individual, however, the nerve of the left side extended down the cord only to the level of the fifth cervical nerve, that on the right side agreeing with the findings in the other individuals. In two of the four individuals in which the development of the spinal accessory was symmetrical in the two sides, it was found that the ramus communicans given off from the sixth cervical nerve contained a very few scattered medullated fibers. That from the seventh nerve however, contained a large number of white rami fibers. In the fifth animal, in which the development of the spinal accessory was unsymmetrical, sections were made of the anterior roots of the spinal nerves after treatment with osmic acid, but unfortunately the rami were not studied, and as regards the anterior roots, it was not found possible to make a count of the smallest fibers, which could be regarded as sufficiently accurate for record. It was certain, however that a marked increase in the number of these fibers occurred in a definite anterior root on each side and this increase was correlated with the level of the lowest root of the spinal accessory. Thus it was found that on the left side, on which the spinal accessory descended to the level of the fifth nerve, the sudden increase of small fibers occurred in the anterior root of the sixth nerve, while on the right side, in which the access ory descended to the level of the sixth nerve, the increase did not occur until the seventh nerve. These relations may be expressed in tabular form thus: Left side Level of lowest root of spinal Anterior root in which increase of small fibers occurs. accessory. These observations in the cat are by no means so conclusive as those made upon the rat, but nevertheless they harmonize admirably with them, and the case of the fifth cat is especially interesting as showing that the correlation of the white. rami fibers with the origin of the lowest root of the spinal accessory nerve occurs even in cases of individual variation. ADDENDUM. From the above observations there appears to be, in both the rat and the cat, a sudden increase in the number of white rami fibers in the ramus communicans of the nerve which immediately succeeds the last root of the spinal accessory nerve, and the conditions demanded by GASKELL'S supposition are fulfilled. It does not, however, necessarily follow that the significance which GASKELL assigns to the spinal accessory is the correct one. It may be true that the cranial lateral motor roots are serially homologous with the visceral motor roots, i.e., the white rami fibers of the cord; indeed, there is much to recommend such a view. But that the spinal accessory, or to be more precise, the cervical portion of that nerve, actually represents the white rami fibers of the upper cervical spinal nerves is more than doubtful. It is becoming more and more apparent that the classification of the spinal accessory as a distinct unit in the series of cranial nerves is erroneous; it is rather merely a portion of the vagus, whose continuation down the spinal cord is no more remarkable than the downward extension of the spinal tract of the trigeminus. It is true that the fibers of the latter nerve pursue their downward course in the substance of the central nervous system, while the spinal accessory fibers emerge from the cord, but it must be remembered that in the one case the fibers in question are afferent and in the other efferent in quality. In all its morphological and physiological characters, especially when studied from the comparative standpoint, the accessory is closely related to the vagus, and the view, so strongly supported by FÜRBRINGER, that the accessory is really a portion of the vagus, its nucleus being merely a downward extension of the vagus nucleus, seems to represent the true significance of the nerve. Whether or not the downward extension of the vagus nucleus be dependent upon the development of the trapezius and sterno-mastoid muscles, as the evidence presented by FÜRBRINGER seems to indicate, it is certain that comparative anatomy shows us a gradually increasing size of the vagus nucleus and its gradual extension into the spinal region. What the cause which determines the direction of the extension may be is at present unknown, but it is to be noted that the motor vagus nucleus is a lateral nucleus and its direct prolongation downward would therefore bring it into most intimate relation with the cell column from which the spinal white rami fibers take their origin. In its continued downward progress it may be supposed that it would gradually displace the majority of the cells of the sympathetic column throughout the spinal segments it traversed, forcing them to a lower level, so that throughout the region occupied by the extended nucleus, white rami fibers would be either wanting or few in number, while below the termination of the nucleus there would be a sudden increase in their number. This is exactly the condition which the results recorded above seem to show. There is one point, however, which such an explanation fails to clear up, namely, the existence of a second somewhat sudden increase in the number of white rami fibers in connection with the first and second thoracic nerves. The fact that this second outflow begins at about the level of the lowest nerve participating in the formation of the brachial plexus, and that it ceases at about the level of the beginning of the lumbo-sacral plexus, has suggested its dependence in some way upon the plexuses, a view which has been especially emphasized by HARMAN with reference to the upper limits of the outflow. The exact significance of the interdependence remains, however, obscure; but granting its existence, it still leaves room for the significance which has been assigned above to the upper outflow, and it would seem that there are two factors influencing the occurrence of white rami fibers in the cervical region, one of which is the development of the spinal accessory nerve, while the other is associated with the development of the brachial plexus. J. PLAYFAIR MCMURRICH. T. L. W. Bischoff. Literature. 1832. Nervi Accessorii Willisii Anatomia et Physiologia. Heidelbergae. 1832. Francois Franck. 1878. Sur l'innervation de l'iris. Marey's Travaux de Laboratoire, IV. M. Fürbringer. 1897. Ueber die spino-occipitalen Nerven der Selachier und Holocephalen und ihre vergleichende Morphologie. Gegenbaur's Festschrift, 1897. W. H. Gaskell. 1886. On the Structure, Distribution and Function of the Nerves which innervate the Visceral and Vascular Systems. Journ. of Physiol., VII, 1886. 1889. On the Relation between the Structure, Function, Distribution and origin of the Cranial Nerves, together with a Theory of the Origin of the nervous System of Vertebrates. Journ. of Physiol., X, 1889. N. B. Harman. 1900. The Anterior Limit of the Cervico-thoracic visceral efferent Nerves in Man. Journ. of Anat. and Physiol., XXXIV, 1900. J. N. Langley. 1892. On the Origin from the Spinal Cord of the Cervical and Upper Thoracic Sympathetic Fibers, with some Observations on white and gray Rami Communicantes. Philos. Trans. Roy. Soc., CLXXXIII., 1892. F. Nawrocki and J. Przybylski. 1891. Die pupillenerweiternden Nerven der Katze. Arch. f. Physiol. L, 1891. Both daily observation and numerous expressions in literature indicate the highly developed emotional life of birds. All other lower animals, even dogs, are inferior to them in this regard. Desiring to investigate this interesting subject, I undertook an experimental study of the respiratory reactions of the pigeon, an animal which is easily handled and which readily adapts itself to laboratory confinement. As a process through which to study mental phenomena, breathing combines two important advantages: first, it is variable, being highly sensitive not only to changes of the blood, but also to impulses from the peripheral or from the central nervous system; and, secondly, its alterations may be easily recorded pneumographically. The value of the pneumograph 'The physiology of respiration is well summarized by STARLING in SCHAEFER'S Text-Book of Physiology, II, 274-312. |