552 
On Reciprocal Innervation of Antagonistic Muscles: Twelfth 
Note.—Proprioceptive Reflexes. 
By C. S. SHERRINGTON, D.Sc., F.R.S. 
(Received August 10,—Read December 10, 1908.) 
(From the Physiology Laboratory, University of Liverpool.) 
The following two reactions, observable in the extensor muscle of the knee, 
appear not without importance for the reflex co-ordination of antagonistic 
movements at that joint. They are reactions favourably studied in decere- 
brate rigidity. The cat is the animal in which, under that condition, my 
results have been chiefly obtained. | 
The reactions can be observed as follows:—In the decerebrate animal a 
preparation of the extensor of the knee is so made that by detachment of 
other muscles, or severance of other nerves, the vasto-crureus muscle, with its 
nerve-branch from the anterior crural trunk, remains the sole nerve-muscle 
component intact in the whole limb. The vasto-crureus is one of those 
muscles which, after decerebration, exhibits the marked tonus characteristic 
of decerebrate rigidity. This tonus of the vasto-crureus then maintains the 
knee in an attitude of partial or complete extension. The flexor muscles of 
the knee, together with all the other muscles acting on that joint, have been 
paralysed by section of their nerves. 
I. If the nerve of one of the flexors, eg., of semitendinosus, be now 
faradised distal to its place of severance, the stimulation of the motor fibres 
in it causes contraction of the flexor muscle, the knee is consequently flexed ; 
the flexor muscle, by its stronger contraction, bends the knee in spite of the 
tonic contraction going on in vasto-crureus, the extensor muscle. On discon- 
tinuing the faradic stimulation of the motor nerve of the flexor, the flexor 
muscle, of course, ceases to contract. It is then seen that, although the flexor 
is no longer acting, the knee still continues to remain flexed. In other words, 
the tonic contraction of the extensor of the knee, which prior to the con- 
traction of the flexor kept the knee extended, ceases to do so after the 
movement of knee-flexion has been executed. Evidently the forced stretch 
given to the knee-extensor by the contraction of its antagonistic muscle has 
produced some change in the tonic condition of the knee-extensor. It has 
been previously shown* that centripetal impulses from the knee-flexor can 
cause a reflex inhibition of the knee-extensor. But in the experiment now 
described no centripetal impulse from the knee-flexor can have caused the 
* Sherrington, ‘ Roy. Soc. Proc.,’ vol. 52. 
