70 



Mr. C. S. Sherrington. 



[Mar. 17, 



with chloroform and ether. The excitations of the roots have been 

 made in the spinal canal ; the single root, or a component filament 

 from it, has been isolated in the case of the lower roots of the cat and 

 monkey, to a length 5, 6, or 7 cm., and lifted np by a silk ligature on 

 to small platinum electrodes sheathed almost to the points. Series 

 of weak induced currents have been used for excitation, one pint 

 Daniell being in the primary of the ordinary physiological indue- 

 torium (R. Ewald's pattern). The secondary coil has usually been 

 at a distance from the primary somewhat more than twice that at 

 which a current was detectable by the tongue. Use has also been 

 made of absolutely minimal stimuli, and largely of mechanical 

 stimuli. For certain purposes, stimulation by quite strong electrical 

 excitation has been used. 



In these experiments ifc became clear that the frequency of indi- 

 vidual variation, as regards the anatomical and physiological consti- 

 tution of the efferent roots of the lumbo-sacral region, was great 

 enough to demand the recognition of a " pre-axial " and a "post- 

 axial" class of innervation for each muscle and movement. By 

 pre-axial class of innervation is meant that the roots connected with 

 the muscles and the movements are more pre-axial than the roots 

 connected with the same muscles and the same movements in the 

 post-axial class of innervation. 



Thus, in the frog there is a pre-axial class of innervation for the 

 hind limb, in which, for instance, the viith spinal root, as well as sup- 

 plying the antero-internal thigh muscles, supplies the muscles on the 

 front of the leg (tibialis anticus). There is a post-axial class in which 

 the pretibial muscles are supplied by the viiith and ixth roots only. 

 The post-axial class as measured in this way is the more usual. This 

 may be merely because the above criterion, found convenient for dis- 

 tinguishing in any individual case the direction which the variation 

 has taken in it, does not coincide with the mid point about which 

 individual variation in the species is really oscillating. 



By " pre-axial " and " post-axial " classes it is not intended to imply 

 that in the range of individual variation one case is not more fre- 

 quently exemplified than are others ; it is only meant that so frequent 

 is the variation that no one case is sufficiently predominant to warrant 

 the choice of it as a "normal" type, and that therefore it is more 

 correct to treat the composition of the plexus of the species as mul- 

 tiple and then for convenience divide it into classes. I have thought 

 two classes, "pre-axial" and "post-axial," a distinction sufficient to 

 observe in my present description. Just as in the frog, so in the 

 other animals employed, the " pre-axial " and " post-axial " class of the 

 plexus have both been exemplified by individuals of each species. In 

 the rat, rabbit, ca f , and dog, the 9th subthoracic root sometimes sup- 

 plies the intrinsic muscles of the foot (post-axial innervation), some- 



