Page:Proceedings of the Royal Society of London Vol 60.djvu/443

Rh nerve-trunks, the comparison of sensory overlapping with motor overlapping, the relation of overlapping to acuteness of sensation: individual variation, its extent and frequency, as far as can be judged from the skin-fields. Comparison between the human brachial plexus and that of Macacus is made, and it is pointed out that the human plexus is slightly prefixed, as compared with that of Macacus.

Finally, in Section TV, “ shock,” and various spinal reactions are examined, especially with reference to their effects upon the size and other features of the areas of the root-fields, &c., and the results collated and discussed.

A phenomenon came under my observation in the course of experiments upon monkeys at the commencement of the present year which seems sufficiently interesting to merit record here. Its occurrence, so long as certain conditions of experiment are maintained, appears regular and predictable.

Although the character of the movements executed by the skeletal muscles when excited reflexly through the medium of the isolated spinal cord is variable, one feature common to them is their comparative brevity of duration. Many of them are, as pointed out by Fick and by Wundt years ago, hardly distinguishable in several particulars from the simple twitches elicitable from an excised muscle, so brief and local and inco-ordinate do they appear to be. Others are moie prolonged, and, as I have described in a paper recently communicated to the Society, exhibit various forms of sequence or “ march” (Hughlings Jackson). Without recapitulating the conclusions there drawn from the data given in that paper, I wish here to merely point out that of movements due to purely spinal reflex action, although some are fairly extensive, most are quite shortlasting, and not so prolonged as the longer of those that can be elicited under appropriate conditions from the cortex cerebri; also that if prolonged they, like the final phase of prolonged movements initiated from the cortex, tend to become clonic, or to exhibit that kmd of action which in the paper referred to above I have desicr. nated “ alternating.”

The reflex movements, the subject proper of this note, are, on the contrary, of extremely prolonged duration, and absolutely devoid of clonic character and of alternating character. If the cerebral hemi