1892.] On the Nerve-roots of the Lumbosacral Plexus. 77 



mentally distinct portions of the limb, are not regarded as such in 

 the segments of the spinal cord. 



If the simple movements (flexion, &c.) of the limb-joints be con- 

 sidered individually, the region of representation in the spinal roots of 

 Macacus extends for each into at least three segments of the cord. 

 The region of representation for each simple movement is abont as 

 extended for the small joints (digits) as for the large (hip-knee). 

 The whole region of representation for the movements of the knee is, 

 however, longer (includes more cord segments) than that for the 

 ankle ; and that for the hip is longer than that for the knee. This 

 is because the more distal the joint the greater the overlap of the 

 regions of representation in the roots of each of the two opposed 

 movements at the joint. Of the opposed movements, the one which 

 is in a direction toward the anterior aspect of the limb is always 

 represented the more pre-axially in the spinal roots. 



In the thigh, the nerve-roots supplying the musculature are none 

 of them common at once to the muscle groups of the anterior and 

 posterior aspects of the thigh. In the foot and leg the nerve-roots 

 supplying the muscles each supply muscles situated both on the ante- 

 rior and posterior aspects ; this is more marked in the case of the 

 foot than of the leg ; yet in the former even the musculature of the 

 sole is distinctly post-axial to that of the dorsum. 



Although there is clear evidence that the nerve supply of the 

 skin of the hallux is pre-axial to that of the 5th digit, my experi- 

 ments have given only equivocal evidence that the musculature of 

 the hallux is pre-axial to that of the minimus ; nor is in the thigh 

 the gracilis (lower part) pre-axial to the vastus externus. The 

 mutual relationship of gracilis and vastus externus is as that of 

 rectus abdominis to erector spinse in the trunk, i.e., ventral to dorsal ; 

 the same is probably true of hallux and 5th digit (as regards their 

 musculature). This is in accord with Paterson's* views of the- 

 mutual relationship of the obturator and anterior crural nerves, 

 although not with his extension of a similar view to the relationship 

 of the internal and external popliteal nerves. 



The posterior aspect of the thigh and leg afford an important ex- 

 ception to the rule given by Forgue and Lannegrace, and confirmed, as 

 regards the fore-limb, by Herringham, viz., that, of the superficial 

 and deep muscular layers of a region of the limb, the superficial layer 

 is innervated by more pre-axial roots than the deep layer. The 

 reverse holds good for the calf muscles and the hamstrings. 



The significance of the distribution of the efferent fibres of a spinal 

 root is, as J. Miiller suggested, anatomical (based on metamerism,. 

 &c.) rather than functional (based on co-ordinate action, &c). Ex- 

 citation of an entire efferent root produces a combined movement 



* ' Jl. of Anat. and Physiol.,' 1887 and 1889. 



