Page:Proceedings of the Royal Society of London Vol 60.djvu/448

416 be obtained by electrical excitation of the tra c t in tbe crura cerebri, when, as sometimes happens, th at excitation evokes flexion at elbow or at knee. This and the previous fact which evidences th at the result is obtainable after complete removal of the whole cerebrum bear out the view arrived at in my former paper th at for this reciprocal and, as I believe, elem entary co-ordination, it is not essential th a t “ high le v e l” centres (Hughlings Jackson) be employed. I incline to think, however, th at this kind of co-ordination at elbow and knee is probably largely made use of in movements initiated via the cerebral hemispheres as well as in the lower reflexes, on the observation of which the present Note is based. This conclusion is indicated by its occurring in response to excitation of the pyramidal fibres in the crura. In the case of the reciprocal innervation of antagonistic ocular muscles I was able to prove th a t it took place even in “ willed movements.” It seems, in view of what has been shown above, legitim ate to extend th at result to the additional examples afforded by elbo.w-joint and knee.

Regarding the innervation of the triceps and quadriceps extensor cruis, it is interesting to note th at these muscles, which are of all among the limb muscles particularly difficult to provoke to action by local spinal reflexes, are the very ones which, when the level of the transection is pontial or prepontial, exhibit tonic contraction the most markedly. The well-known and oft-corroborated Sanders-Ezn phenomenon of inaccessibility of the extensors of the knee to spinal reflex action has, as I have recently shown, certain limitations, but a t the same tim e so long as the transection is spinal— even when carried out so as to isolate not merely a portion of, but the whole, spinal cord entire from bulb to filum term inale—does apply very strictly to excitations arising in its own local region proper. And the spinal reflex relations of the triceps brachii in this respect, as pointed out elsewhere, somewhat resemble those of the distal portion of the quadriceps extensor of th e leg. A lteration of the site of tran ­ section from infrabulbar to suprabulbar levels works a curious change in this. The Sanders-Ezn phenomenon then becomes subject to strik ­ ing contravention. I have, after the higher transection, several times seen excitation of the hind foot itself provoke unilateral ideolateral extension of knee, a result incompatible with the Sanders-Ezn rule even under the lim itations of ideolaterality, &c., which I consider m ust be attached to it. And similarly w ith the triceps at the elbow.

The difference between the accessibility of the quadriceps to reflex action after infrabulbar and after suprabulbar transection may, however, be less abrupt than it appears at first sight, and a superficial rather than a fundam ental distinction. W hen extensor rigidity has ensued at elbow and knee after suprabulbar transection, the reflex excitability of triceps brachii and quadriceps cruris seems in a man-