EMPLOYMENT OF CHLOROFORM IN A DIFFICULT LABOUR
122 cerebro-spinal axis; but it is easy to see, when the tuber annulare has been cut through in its whole thickness, from right to left, that all the superficial stratifications, (by which it is characterized,) as also those placed more deeply, emanate from the median portion of the anterior stratification. The superficial and the deep fibres differ one from another only in their relative position to the corpora pyramidalia, in their course through the pons."* The decussation of these arciform
... of these arciform fibres of the pons Varolii explains why lesions of the cerebellum, when so deeply seated as to affect the primary planes of fibrous matter on the central stem, have the same crossed effect as those of the cerebrum. The explanation of this fact, as offered in a recent work upon physiologyt appears to me hardly sufficient. " This is not so obviously explicable as the similar instance of the cerebrum, for the cerebellar fibres of the medulla oblongata (restiform bodies) do not appear to decussate. Yet it seems scarcely necessary, in order to explain the I phenomenon, to have recourse to the supposition that they do decussate. The close connexion between the restiform bodies and the pyramids, by means of the arciform fibres, renders the latter exceedingly liable to sympathize with the condition of the former, and therefore prone to propagate the morbid influence to the opposite half of the spinal cord, and through that to the opposite half of the body. It must be borne in mind, that some of the fibres of the anterior pyramids very probably derive their origin from the central grey matter of the medulla oblongata, as well as of the mesocephale, and that some at least of those which affect the right half of the cord probably derive their origin from the left side of either or both of those segments of the encephalon. That lesion of one hemisphere of the cerebellum may influence the corresponding half of the medulla oblongata is likely, from the connexion which the restiform fibres establish between them."t A more satisfactory explanation of the " crossed effect" upon the body of lesions of the cerebellum may surely be deduced from the fact, that the antero-posterior fibres of the medulla oblongata, and the arched fibres of the mesocephale, or pons Varolii, here described, decussate along their whole line of origin, from the anterior cranial prolongation of the spinal cord. the corpus callosum, unless we restrict the term to those superficial transverse fibres which connect one cerebellar lobe with the other. It is a highly developed portion of the anterior stratifications of the cord. Vesicular matter is accumulated in considerable quantity; white fibres pass forwards towards the quadrigeminal bodies and the cerebral hemi-* Exposition Anatomique de 1'Organisation du Centre Nerveux, par Nathalis Guiilot, p. 200. t Todd and Bowman's Physiology, vol. i. p. 272. : Op. cit. p. 272. spheres, downwards to the spinal cord, and transversely or obliquely outwards to either lobe of the cerebellum. Besides the superficial transverse commissural fibres of the pong, there are others, deeper and not always symmetrical, nor always to be found pursuing precisely the same course; some connect the crura cerebelli with the crura cerebri, or with the pyramidal bodies; others form a transverse loop, uniting the two restiform bodies before they pass into the cerebellum. Ceasing, then, to regard the pons Varolii as an analogous structure with the corpus callosum, we should view it as a highly developed portion of the cerebro-spinal axis, where, amidst an accumulation of vesicular matter, the stratifications of the cord so arrange themselves that they may pass into the different ganglia of which the encephalon is composed; and where fresh fibres take their rise, for the purpose of bringing distant parts into connexion.