the Lumbo-Sacral Plexus of Macacus rhesus. 251 



limb, owing to the arrangement of the muscles as has been explained 

 above. So troublesome was this action when the movements at the 

 wrist and digital joints were being studied, that an instrument was 

 devised to exclude the action of the triceps under these circumstances, 

 In the posterior extremity, the action of the quadratus femoris 

 tends to produce, besides extension at the knee, extension at the ankle 

 and of the digits. This action of the extensor muscle of the knee, 

 though well marked in the dog, is much less so in the monkey, so 

 that an assistant could fix the limb in such a position as to exclude 

 this action without the aid of an instrument. It is obviously of 

 great importance that this action of a muscle indirectly upon joints 

 on which it has no direct action should be clearly recognised in all 

 investigations of the movements at a given joint when any single 

 nerve root is stimulated. If one muscle can directly or indirectly 

 produce movements at so many joints, it is clear that we must first 

 eliminate indirect effects of the action of this muscle before we can 

 study the movements at these joints, as produced by the muscles 

 which act directly on them, otherwise we should be led into 

 error. 



Operative Procedure. 



a. Operation. In every experiment the animal was narcotised by 

 causing it to inhale ether ; it was kept deeply under the influence of 

 the anaesthetic during the whole of the experiment, and killed by an 

 overdose of it at the end, except in those experiments in which the 

 animals were allowed to live for some weeks for the study of the effect 

 of section of nerve roots on its mode of progression and standing, 

 and also to allow sufficient time for the degeneration in the peri- 

 pheral nerves, consequent on such section of a nerve root, to develop. 

 In these instances the operation, which was always a very trivial 

 one, was done under strict antiseptic precautions, and the small 

 wound afterwards dressed antiseptically. The animals were, of 

 course, narcotised in these as in the other class of experiments. The 

 neural canal was first opened, a ligature passed round the motor and 

 sensory portions of a given nerve root together, as close to the 

 spinal cord as possible, after which the two portions of the root were 

 divided between the ligature and the cord. When the separate 

 bundles of nerve fibres of which a nerve root is composed were 

 under investigation, the whole root was dissected out to a varying 

 distance beyond its point of exit from the neural canal, so as to allow 

 of each separate bundle being separated from the others contained in 

 a nerve root, for as long a distance as possible, in order to prevent 

 diffusion of the current from one bundle of nerve fibres to another 

 during the excitation experiments. 



In those experiments in which the muscles were exposed by dis- 



