the Lumbo-Sacral Plexus of Macacus rhesus. 269 



terminal segments are reached, when extension is represented at a 

 higher level than flexion in both instances. This is, however, not 

 strictly accurate, for dorsiflexion at the ankle is strictly analogous to 

 extension at the wrist ; which leaves two joints alone at which there 

 is any discord, viz., the elbow and knee. 



It is possible by stimulation of a single bundle of fibres in a nerve 

 root to produce contraction of a single muscle and it alone ; but this 

 effect is easier to obtain in the case of the cervico-dorsal roots which 

 enter into the formation of the brachial plexus than it is in the case of 

 the roots which combine to form the lumbo- sacral plexus, owing to the 

 difficulty of isolating the separate bundles of nerve fibres of which the 

 roots are composed for a great enough distance of their course after 

 their exit from the neural canal, and before they unite to form the 

 plexus in the case of the lumbo-sacral roots. The same muscle is 

 always represented in more than one nerve root, usually two, and to an 

 unequal extent in these. The only muscle which I have met with which 

 is not represented in more than one nerve root is the tensor fasciae 

 femoris; and this agrees with Sherrington's observations with regard 

 to this muscle. In corning to the conclusion that the rule is that a 

 single muscle is represented in neither more nor less than two nerve 

 roots, I wish it to be clearly understood that this conclusion is based 

 upon the results obtained in any single individual of a class under 

 observation. That, owing to variations, the same muscle may be 

 found represented in three or even four nerve roots, I do not pretend 

 to deny ; but what I contend is that in the majority of instances a 

 single muscle is represented in two nerve roots, and that when a 

 variation is met with with regard to this muscle, it is, as a rule, that 

 one of the nerve roots in which it is represented is different, rather 

 than that it is represented in more nerve roots. 



When the same muscle is represented in two nerve roots the 

 muscle fibres innervated by one root are not innervated by the 

 other ; so that only part of the muscle contracts when a single root 

 is excited. This part of the muscle may be either one end of it, one 

 lateral half of it, or a superficial or deep part of it, as the case 

 may be. 



Ablation Experiments. 



Division of any given nerve root produces paresis of the group of 

 muscles supplied by it, which paresis is temporary, nearly all of it 

 being recovered from. The amount of paresis or paralysis produced 

 is proportional to the number of nerve roots divided; and this again 

 varies according to whether the roots divided are consecutive or 

 alternate ones, the effect being much greater in the former than in 

 the latter case. That such should be the case is only what was to be 

 expected, for section of any two consecutive roots cannot fail to cause 



