THE SPINAL ANIMAL 
37 
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modulates and helps to guide and control 
the nicety of the movement. I liave shown 
that in spinal and in bulbo-spinal reactions* 
(Fig. i), and also in many cortical t (Fig. 2), 
the reverse is in reality the condition of the 
antagonist. It is, in fact, relaxed by in- 
hibition of its tonus and of any pre-existent 
contraction, at the same moment as the Fig. 2 
opposed muscle is by pressor influence thrown into contraction. For instance, when the 
motor neurons of the flexor muscles of the elbow are excited by pressor influences in a 
spinal reflex, the motorneurons for the extensor muscles are simultaneously inhibited as a part 
of the same spinal reflex (Fig. 3). But not only are certain movements about a single joint 
opposed one to the other, certain move- 
ments at one joint are opposed to certain 
movements at neighbouring joints. Thus 
the extensors of the knee may be called 
antergetic not only to the flexors of the 
knee, but also to the flexors of the hip 
(Fig. 4). In such cases the 'reciprocal in- 
nervation,' as I have ventured to style this 
mode of co-ordination, still holds good. 
The groups of motor neurons selected by 
the reflex action, as it irradiates over spinal 
segments lying apart in the limb series, are still thoic of synergetic muscles. For instance, while 
the reflex movement evoked by excitation of the fourth lumbar root, or that responsive to the 
long saphenous nerve, usually primarily contracts the flexors of the hip, it involves next, not 
the antergetic muscles in the nearest spinal segments, {e.g. vasti and crureus), but inhibits these 
and embouches into the synergetic of more distant segments, e.g. the hamstring muscles. In this 
way the reflex action, by its 'spread,' develops 
a combined movement — synthesis a har- 
mony.J The mere inspection of a movement 
without further analysis of it is a very insecure 
guide toward judgment whether it be co- 
ordinate. The joints and muscles of the limb 
have been evolved contemporaneously and 
together in the course of the history of the 
individual and of the species. No muscle can 
therefore be thrown into action which will 
Fig. 3 
* 'Journ. of Physiol.; vol. xiii, 1892. J .phUos. Trans. Roy. Soc.,' 1896. 
t 'Proc. Roy. Soc.,' vol. lii, 1893. See also Hering an.l Sherrington, 'Pfliiger's Archiv,' 1897. 
