bh) 
a simple cortical impulse is given from a cortical centre to a lower 
one — probably in the thalamus — from which synchronous im- 
pulses are given to both extremities. For each step an impulse is 
necessary and in walking we get a succession of impulses alter- 
nately from the right and the left hemisphere, but each of them 
working on museles of both legs. We may suppose that one centre 
innervates the contra-lateral extensors as well as the homolateral 
flexors. This means that a stimulation of the cortical centre causes 
a tetanic contraction of the contralateral extensors, hypotony of the 
contralateral flexors and hypertony of the homolateral flexors. Distrue- 
tion of a centre of this kind is followed by hypertony of the 
contralateral extensors and also of the homolateral flexors. With a 
one-sided focus the muscles of the contralateral gastrocnemiusgroup 
are strongly hypertonic, the flexors slightly hypotonic but the muscles 
of the tibialisgroup of the homolateral side are also appreciably 
hypertonic. I think that this also causes the appearance of the 
shortening-reflex, described in a former paper. But at least we have 
also one condition favourable to the appearance of a tibialis clonus. 
As a rule it will not be possible to obtain a tibialis clonus as the 
large muscular mas: of the leg and foot acts as a strongly damping 
factor, which immediately checks any commencement of a tibialis: 
clonus. Only exceptionally, when a second focus in the other hemis- 
phere has caused the appearance of a slight hypertonic state of the 
calf muscles, a commencement of tibialis clonus may be strengthened 
by a triceps clonus, or to an existing triceps clonus may be added 
a rhythmic clonic contraction of the tibialis group. If the second 
focus be an extensive one, the hypertony of the gastrocnemius group 
generally grows so as to entirely suppress the action of the anterior 
muscles. In all my cases the hypertony of the calf muscles was 
very slight. With a strongly hypertonic gastrocnemius [ never suc- 
ceeded in obtaining an alternating clonus. This sufficiently explains 
the rarity of the occurrence of alternating clonus. 
