1881.] The Brachial and Lumbo- Sacral Plexuses. 



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The muscles we observed in action are the gluteal, the adductors, 

 extensor cruris, and the peroneus longus. This latter explains the 

 pointing of the great toe by depression of the base of the first meta- 

 tarsal bone ; and at the same time the raising of the outer edge of the 

 foot. The sural muscles did not appear to contract. 



This apparently involves stimulation of nerves conveyed by the 

 superior gluteal, anterior crural, obturator, and musculo-cutaneous 

 branch of the external popliteal nerve. 



Fourth Lumbar (third lumbar in man). — Flexion of the thigh on the 

 pelvis and extension of the leg. — This brings the leg in the line straight 

 forwards. 



In addition to the ilio-psoas (evidently in action, though not visible), 

 the sartorius, adductors, and extensor cruris were observed to contract. 

 No action was observable in the muscles of the leg or foot. 



The nerves involved are conveyed by the anterior crural and obtu- 

 rator trunks. 



Stimulation of the third lumbar (second in man) caused contraction 

 of muscles in the flank, but no action in the leg. The cremaster muscle 

 was not observed, though its contraction should be expected here. 

 Stimulation of the second (first in man) and of the first lumbar nerves 

 caused contraction of some muscles in the flank and hypogastric region. 



It will be seen that the movements which result from stimulation of 

 the individual roots of the brachial and crural plexuses are not mere 

 contractions, more or less strong, of various muscles (though many 

 muscles are excited to contraction by more than one root, as previous 

 experimenters have found), but a highly co-ordinated functional 

 synergy in each case, as Remak has supposed. 



The muscles thrown into action by each root are innervated in most 

 cases by several nerve-trunks, whence it would appear that the plexi- 

 form junctions of the various roots are for the purpose of distributing 

 the requisite motor fibres in different trunks to the various muscles 

 engaged in each functional combination. 



The result of section of each motor root would, therefore, be 

 paralysis of the corresponding combination, not necessarily, however, of 

 the individual muscles involved. For, as many of these are innervated 

 by more than one root, the degree of paralysis of the muscles would 

 depend on the degree of motor innervation by the root divided ; and, 

 therefore, while weakened, they might yet act in other combinations in 

 so far as they were supplied by other roots. Such appears to us the 

 real explanation of the fact stated by Panizza, that there was no abso- 

 lute immobility of the limb in his experiments until every root was 

 cut. 



It is evident that the cervical and lumbar enlargements of the spinal 

 cord are centres of highly co-ordinated muscular combinations. These 

 (as Krause's researches on rabbits, compared with ours, would seem to 



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