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THOMPSON YATES LABORATORIES REPORT 
and hallux. The skin of pollex and hallux themselves and of radial and tibial sides of palm and sole yield 
the reflex less readily ; their skin is innervated from spinal levels segmentally less close to musculature of 
pollex and hallux. 
In Monkey and in Cat excitation of the Vllth or Vlllth thoracic afferent root by absolutely 
minimal stimuli, evokes often contraction in the muscles of the Vllth (or Vlllth) intercostal region, and 
not in other intercostal : contraction in intercostal spaces other than Vllth (or Vlllth) is never obtained 
without contraction in that space. 
An exception to this rule seems offered by the pinna : excitation of the pinna (Cat) evokes 
retraction of it ; afferent nerves are Vth cranial, and 1st and Ilnd cervical. The motor nerve 
seems to be the Vllth cranial. The reflex continues well after section of the Vth cranial and 1st 
cervical ; the reflex then involves discharge from the Ilnd cervical into the Vllth crainal, i.e., the 
primary reflex is pluri-segmental. 
Pluri-segmental Reflex Arcs of Low^ Resistance 
At the same time, as I have previously pointed out,* there co-exists for most afferent roots, 
together with their own uni-segmental paths of minimal resistance, other spinal reflex paths which 
extend beyond the limits of the afferent root's own segment, both upwards and downwards, and 
yet offer a resistance not with certainty demonstrable to be greater than that of the low resistance 
path confined to the one segment. 
Examples. — Stimulation of central end of palmar digital nerve on ulnar side of little finger evokes 
flexion and adduction of thumb. Similarly, excitation of palmar digital of radial side of index gives 
same movement. Section of Vlllth cervical afferent root does not obviously change the reflex. Section 
of the 1st thoracic motor root does not necessitate a stronger excitation of the little-finger nerve to evoke 
the movement. Section of the Vllth cervical motor root does not necessitate a stronger stimulation of 
the index digital to evoke the movement. Section of the Ilnd thoracic does not modify the reflex. 
Section of the motor root of Vlllth cervical finally abolishes the reflex, i.e., the reflex flexion of thumb. 
The reflex path was not appreciably more resistant when it passed from 1st thoracic into Vlllth cervical, 
or from Vllth cervical into Vlllth cervical, than when confined entirely to 1st thoracic segment or to 
Vllth cervical segment. 
Excitation of skin near orifice of vagina elicits protrusion of anus. The afferent roots of the Xth 
and Vlllth post thoracic nerves are now cut. Excitation, i.e.., a pinch of the skin as before, still elicits 
the protrusion of anus ; the patent afferent root is therefore the IXth ; the IXth ventral root is cut ; a 
pinch as before still elicits the anal protrusion as readily as before. Similarly, using the roots of the opposite 
side in the same animal, excitation of the IXth post-thoracic afferent root with 20 k.s. just elicited anal 
protrusion, the motor root of IXth was then severed, whereupon IXth afferent root still evoked well a 
protrusion of anus. In the latter part of the experiment the possibility of a uni-segmental crossed reflex 
is eliminated. 
For further examples reference can be made to my ' Lumbo-sacral Plexus.' 
Functional Solidarity of the Motor Cell-groups for certain Groups of Muscles. 
In such instances as these, centripetal impulses poured into one spinal segment evoke cen- 
trifugal impulses in adjacent segments, without demonstrably greater difliculty than when confined 
to the actual segment into which they were themselves thrown. Irradiation appears to meet with 
no increase of resistance when passing from one segment to another in these cases. The 
solidarity of these parts of the essentially segmented cord must be extraordinarily complete. The 
* ' Journ. of Physiol.,' 1892, lac, cit. 
