EXAMINATION OF SOME SPINAL NERVES 149 
This inequality of excitability via local reflex paths, evidenced by the motor neurons of 
muscles acting antergetically about a joint, is not similarly great for all joints ; thus, the inequality 
between flexors and extensors of knee seems certainly greater than between extensors and flexors 
of hip, and than the inequality between extensors and flexors of elbow. It is not to be forgotten 
that this inequality may be less an inequality of accessibility to impulses or influence, than an 
inequality of distribution of excitor impulses, influence being brought to bear on the other 
neurons, but in the sense of ' inhibition, as is certainly the case in some instances (see pp. 165, 
166). It is significant that the arrangement is not that all the muscle groups about one joint are 
relatively inaccessible, and all the groups at another joint accessible, but that the diflference is 
between antagonistic groups acting about one and the same joint. 
Quite in accord with their difference in degree of approachability by local afferent 
channels of short paths, is the difference of degree of amenability to local play of tonic influence 
exhibited by various sub-groups of motor neurons. In illustration, I give the following : — The 
cord having been transected in the lower thoracic region, the Monkey frequently develops, in the 
course of some weeks, marked rigidity of the lower limbs. Certain muscles become spastic and 
rigid, and gradually cease to be ever fully relaxed, and structural rigidity may in time supervene. 
The hypertonic and rigid muscles are especially the flexors of the hips and of the knees. In five 
months' time, the position permanently assumed by the limbs is as follows : they are drawn up 
and somewhat crossed. The flexion of hips and knees may be extreme, the adduction of the 
thighs is less. I cannot myself escape the conviction that the position assumed by the limb, and 
the late rigidity itself and its distribution in the musculature, is the natural outcome of the fact 
that after the cord had been sundered from the brain the inequality of incidence of the local 
stream of centripetal impulses — and the fact that at its einbouchement it selects, employs, and 
discharges motor neurons for flexion of hip and knee, and neglects the antergic extensors — leads, in 
due course, to a permanent upset of balance between the two, in which relative over-action is 
continuous in the one, and atrophy, yielding and under-action, existent in the other. In one 
Monkey the amount of rigid flexion of the hips and knees was unequal on the two sides, the left 
hip and knee being kept more. flexed than the right: in this animal, reflexes were more easily 
elicited from the skin of the left limb than of the right, but owing to the more rigid condition of 
the left limb, the movement obtained was generally less in the left than right limb. It was, in 
fact, contrary to a rule given (p. 161), easier to obtain movement of the right hip and knee from 
many parts of the skin of the left limb than from the skin of right itself. From the front of the 
left thigh, flexion of the left hip and adduction of the right thigh, with slight extension of the 
right knee, could be regularly evoked. The greater rigidity was, therefore, present in that limb 
which possessed the greater sensitiveness. This supports, therefore, the view of the spinal reflex 
origin of the late rigidity which I here put forward. The same explanation, with little modifi- 
cation, may apply to the later rigidities occurring in limbs, subsequent to lesions of the limb areas 
of the cortex cerebri. After reading the recent admirable account by Hermann Munk,* of 
* 'Sitzb. d. Kbnigl. Akad. d. Wiss. zu Berlin,' 1895. 
