, EXAMINATION OF SOME SPINAL NERVES 167 
of the extensors, and at the same time some contraction of the flexors. In each case the 
phenomenon is one of regular occurrence so long as the conditions are regularly repeated. This 
leads me to return to the phenomena mentioned above at p. 160. These, in illustration of the 
existence of the long uncrossed paths in the bulbo-spinal axis, pass from bulb and cerebellum, even 
through great lengths of the cord. It is obvious that for evidence of inhibition it is supremely 
important to have a steady condition of activity pre-existent in the tissue to be examined. 
Inhibition in muscle has for its sign relaxation. Relaxation predicates contraction, tonic or 
otherwise. Upon prepontine transection (Rabbit, Cat) ensues what I have termed above decerebrate 
rigidity^ which affects the extensors of knee, elbow, and back, and to a less extent ankles, but not 
wrists, and includes neck and tail pre-eminently. Hughlings Jackson has laid stress on the 
cerebellum as a source of muscular tonus. In the phenomenon of 'decerebrate rigidity' the 
cerebellum may be an ultimate source of the rigidity, and right-hand semi-section of the bulb above 
the decussation of pyramids destroys the right-hand rigidity. It must arise from an uncrossed 
influence arising somewhere above the lowest third of the IVth ventricle, and below the cerebral 
hemispheres. The state of contraction appears akin to ordinary tonus. Its reflex origin is evidenced 
by its severe or even total depression on severance of appropriate afferent spinal roots (p. 148). 
Thus the hypertonic condition of rigidity almost or quite vanishes from left triceps when the left 
afferent brachial roots are cut, from left quadriceps extensor cruris when left lumbo-sacral afferent 
roots are cut. The rigidity is a persistent condition for many hours ; I have seen it persist for four 
days. It is so forcible that the animal can be placed erect on the four feet. Semi-section of cord 
abolishes it on the same side below the lesion, so also does semi-section of the bulb above the 
pyramidal decussation. It is lowered or temporarily abolished by deep chemical anaesthesia, 
sufficient to abolish ear-reflex (Cat) or knee-jerk. With this hypertonic rigidity as background, 
inhibitions, relaxations, can be produced in these muscles. The graphic records taken in the 
ordinary way show that the excitations which reflexly cause contraction of the flexors, cause 
synchronous relaxation — often even to post-mortem length — of the extensor muscles. Thus : 
from skin of fore-paw, from dorsal cutaneous branch of ulnar nerve, from funiculus cuneatus at 
the calamus, from side of superior vermis, contraction of biceps, relaxation of triceps of same side ; 
from hind-paw, from internal saphenous nerve, from funiculus gracilis, side of superior vermis, 
contraction of the hamstrings, relaxation of the quadriceps extensor cruris of same side. At the 
crossed elbow occurs (Rabbit, Cat, Dog, Monkey) conversely, some relaxation of flexors of knee 
and elbow, and increase of existing contraction in extensors. At the crossed knee, similarly, occurs 
(Cat, Dog, Monkey) extension (with extension of ankle), that is, increased contraction of extensors 
with further relaxation of flexors ; but in Rabbit, in my experience, flexion at the crossed knee 
concurrently with flexion at the same side knee, and some extension at both ankles is the rule. 
The concurrence in reply to one and the same excitation of inhibition of one component of an 
antergetic couple, with contraction of the other component, occurs in these instances as in the 
reactions of the lateral eye-muscles.* It is indeed a complete example of what I have described 
as ' reciprocal innervation.' 
' Proc. Roy. Soc.,' vol. 52, 1892. Sherrington ; and 'Journ. of Physiol.,' vol. 17, 1894. 
