EXAMINATION OF SOME SPINAL NERVES 139 
further. The reflex apparatus of the cord may be usefully considered in five regions, for the (i) tail, 
(2) pelvic limb, (3) trunk, (4) brachial limb, and (5) neck, each of these regions being double, 
because made of right and left component regions. I would consider 'short' any paths which 
are entirely confined to a single one of these main regions. These main regions I separate as 
' spinal regions,' on account of their each possessing a certain degree of physiological solidarity. 
Short Spinal Reflexes. 
The following rules refer almost exclusively to spinal reflexes of short paths only — i.e.^ to 
'short spinal reflexes' — as understood by the above given definition. 
Among inferences that may be drawn from the observations stated above, one dealing with 
the degree of correspondence between the morphological structure and the functional mechanism 
of the cord may be taken first. Broadly speaking, it may be said that the degree of reflex spinal 
intimacy between segments is directly proportional to their segmental proxitnity. 
The fundamental experiment which illustrates this rule is the following : — Cat, the cord 
transected at the 1st cervical level ; the roots of the Vllth thoracic nerve exposed in the vertebral 
canal ; these severed together through the ganglion, well outside the dural sheath ; the central 
end of the mixed nerve, i.e., of both roots in the single sheath, then ligated, held up free, and 
excited with faradic currents ; reflex contraction of the intercostal muscles of the 8th and 6th 
spaces occurs, that of the 8th space is a little more easily obtained than that of the 6th space, i.e., 
with slightly less intense currents. Pinching the central end of the nerve between ivory-tipped 
forceps also evokes contraction in the 6th and 8th spaces ; by pinching 7th, it is usually not 
possible to evoke contraction in intercostal spaces further removed than 6th and 8th ; by sufficient 
increase of intensity of the faradic currents a further spread is possible. By applying the electrodes 
to the cord itself along the dorso-lateral fissure in the region of entrance of the filaments of Vllth 
thoracic, contraction of the muscles in the 8th and 6th spaces is easily produced, but not so easily 
in spaces further removed, though with less difficulty than by excitation of tlie root filaments of 
7th outside. On shifting the electrodes to the line of surface origin of the filaments of the dorsal 
root of Vlllth thoracic, the contraction in the 6th intercostal space at once disappears ; on shifting 
to the surface entrance of Vlth thoracic, the contraction in the 8th space drops out, if not 
completely, very nearly so, but by increasing the intensity of excitation can be regained. The 
amount of intraspinal overlap would thus seem to be in this region about equal in both directions, 
and to start from the segment of the afferent root, excited as from a centre ; but the direction of 
spread is somewhat easier away from the head than toward the head, a significant exception to the 
4th 'law' of Pfluger.* It may be recalled that it was proved in my previous paper that the 
sensory innervation of the skin of most of the trunk is segmentally anterior to the motor 
innervation of the underlying muscles, an oblique relationship existing between them. By 
carefully graduating the degree of excitation the course of the spread from one intercostal space to 
the next seems to be quite recognisably accompanied by increase of resistance of conduction. 
The following are adduced as further examples of the rule of segmental proximity : — 
' Ueber die sensorischen Functionen d. Riickenmarks.' Berlin, 1853. 
