1907.] Innervation of Antagonistic Muscles. 345 



never contraction of these muscles, but is inhibitory relaxation. Similarly, 

 therefore, with the afferent nerves issuing from these muscles, it may be that 

 they contain some fibres which, if stimulated by themselves apart from the 

 other fibres in the nerves, would evoke reflex contraction of the muscles, 

 although the whole collection of nerve-fibres in the nerve-branch causes reflex 

 inhibition of the muscles when the mode of stimulation is faradisation or 

 mechanical compression of the nerve. This possibility is emphasised by 

 other facts. These may be briefly stated as follows : — 



1. The tonic rigidity of vasto-crureus in decerebrate rigidity appears to be 

 reflex, and the afferent channel of the reflex seems to lie in the nerve issuing 

 from vasto-crureus itself. The tonic rigidity of this muscle is maintained when 

 all the nerves of both hind limbs have been severed, excepting only the 

 nerve of the vasto-crureus itself. The rigidity of the muscle immediately 

 ceases on severance of the spinal afferent roots through which pass the 

 afferent fibres of the vasto-crureus nerve itself. Similarly, also, with the 

 tonic contraction of gastrocnemius under decerebrate rigidity, and with that 

 of soleus. The tonic contraction of these muscles ceases only on severance 

 of the afferent fibres issuing from those muscles themselves. 



2. When all the nerves of both hind limbs have been severed, excepting 

 only the nerve of vasto-crureus, squeezing the lower end of the shaft of the 

 femur, exposed from the outer side, after exsection of the middle portion of 

 the length of the shaft, evokes contraction of the vasto-crureus, and this 

 contraction becomes inelicitable on severing the afferent spinal roots of the 

 limb. Similarly, when the popliteal nerve remains as well as the nerve 

 of vasto-crureus, contraction of vasto-crureus is elicited by squeezing the 

 shaft of the tibia, but the reaction ceases on severing the afferent spinal 

 roots of the limb. Again, under decerebrate rigidity, when all the nerves of 

 both hind limbs are severed, excepting only the nerves of gastrocnemius and 

 soleus of one side, light tapping on the shaft of the tibia excites increase of 

 the tonic contraction of gastrocnemius and soleus ; and this persists after the 

 shaft of the femur has been cut through, but ceases on severance of the 

 afferent spinal roots of the limb. 



3. If, under decerebrate rigidity, the animal being in the inverted posture, 

 the hind limb is lightly lifted by the foot into a position of full extension at 

 knee and the foot is then released so that the limb below the knee drops 

 into flexion, the free fall is seen to be suddenly checked much before full 

 flexion is reached. The impression given is that of a contraction reflexly 

 evoked in the extensors of the knee. The reaction occurs when all nerves of 

 both hind limbs have been severed, excepting only the nerve of the vasto- 

 crureus under observation. It ceases when the afferent spinal roots of the 



