

1905.] On Reciprocal Innervation of Antagonistic Muscles. 283 
to it, the tonus is at once and definitively abolished. To sever the afferent 
nerve-fibres of the muscle without interfering with the efferent, it is, of 
course, only necessary to sever the dorsal spinal roots in the vertebral 
canal—these roots in the dog and cat are the 4th, Sth, and 6th lumbar, 
and in the monkey the 3rd, 4th, and 5th lumbar. The reflex tonus of 
this muscle is, therefore, shown in this way to be unquestionably due to 
the nerve arcs arising in and returning to itself only. 
If one of the longer branches of the hamstring nerve be carefully isolated 
and its central end stimulated, the excitation provokes reflex contraction 
in the other hamstring muscles. It never, in my experience, normally 
provokes contraction in the antagonistic extensor of the knee, although it 
does in flexors of the hip, which are anatomically closely connected with 
certain extensors of the knee. If, conversely, the central end of the nerve 
of a pure extensor of the knee, ¢.9., vastus medialis and crureus, be similarly 
‘excited, it does not, in my experience, provoke any primary reflex contrac- 
tion in the antagonistic hamstring muscles. It can, in my experience, 
provoke reflex contraction of the extensor muscle of the knee, but the risk 
of escape of current to the other branches of the nerve, when applying 
electrical stimuli to these branches of the anterior crural, is considerable, 
so that I have resorted to mechanical stimulation, and the reflex effect 
produced by that mode of stimulation of these muscular branches of the 
cruralis is slight. That mechanical stimulation of the extensor of the knee’ 
does induce reflex contraction of the extensor itself is, however, plainly 
demonstrable under “ decerebrate rigidity.” All the nerves of the limb 
being severed, except those to the vasti and crwreus, the animal is inverted 
and the knee then gently but fully extended by raising the foot, the thigh 
being held vertical. The foot is then released, the anticrus falls, and in 
doing so is seen to be suddenly checked by exciting a contraction of the 
extensor of the knee. This contraction is different from a knee-jerk, for it 
only slowly passes off. 
It seems, therefore, that in the case of these two groups of antagonistic 
muscles, the reflex contraction elicitable through the afferent nerve of the 
hamstrings takes place in the hamstring muscles themselves, and does 
not involve the opposed extensor muscle of the knee joint; and that 
the reflex contraction elicitable through the afferent nerve of the extensor 
muscle takes place in the extensor muscle itself, and does not involve the 
hamstrings, the opposed flexors of that joint. 
V. The intimate nature of the process which reveals itself as inhibition 
is admittedly obscure in these reflexes as elsewhere. The present note 
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