337 



On Reciprocal Innervation of Antagonistic Muscles. — 



Tenth Note. 



By C. S. Sherrington, D.Sc, F.RS. 



(Eeceived March 9,— Kead April 18, 1907.) 



(Physiology Laboratory, University of Liverpool.) 



I. In previous notes* on this subject the examples of reciprocal innervation 

 taken from the limb muscles have usually been from muscles acting at the 

 knee. An advantage offered there is that the vasti and crureus, extensors 

 of the knee, act directly on that one joint alone. A muscle acting on two 

 joints is often an extensor of one of the joints and a flexor of the other. 

 When such a muscle is thrown into contraction by reflex action, there may be 

 a dilemma as to whether it is as an extensor or as a flexor that it is acting, 

 and the answer will depend partly on the mode of fixation of the joints at the 

 time. A double-joint muscle of this kind is gastrocnemius; it extends the 

 ankle and flexes the knee. It is, therefore, of interest to examine how this 

 muscle behaves when its antagonist, tibialis anticus, a flexor of the ankle, is 

 thrown into contraction by reflex action. 



Stimulation of any among various points of skin, or of the proximal 

 end of various afferent nerves of the leg, excites reflex contraction of tibialis 

 anticus. A nerve often used for the purpose in my observations has been the 

 cutaneous branch of the peroneal nerve about a centimetre above the 

 ankle (cat). In the reflex which then occurs in the limb, the following points 

 can be made out. The ankle is flexed, and with the flexion of ankle occurs 

 also flexion at knee and hip. If the anterior crural, obturator, hamstring, 

 and popliteal nerve trunks, the insertions of iliopsoas, and psoas parvus, and 

 the origin of pectineus muscles be severed, active flexion of knee and hip 

 are excluded from the reflex. The active flexion at ankle still persists. On 

 inspecting the tendons of the pretibial flexors of the ankle, that of tibialis 

 anticus is seen to be drawn upward at each reflex, and with it also those of 

 extensor longus digitorum and peroneus longus, but in my experience these 

 latter are retracted less. If, in addition to the nerves and muscles mentioned 

 above as severed, the peroneal nerve itself have all its muscular branches 

 severed, but the branch from the popliteal nerve to the gastrocnemius be 

 spared, and that muscle be exposed to inspection, usually no change in that 

 muscle appears. 



* ' Eoy. Soc. Proc.,' vols. 52, 66, 76, 77. 



