NOTES ON MEDIAN AND PAIRED FINS OF FISH. 369 



Experiments on the nerve-supply of the fins. — 

 While occupying the British Association table at the Naples 

 Aquarium last winter, I had the opportunity of conducting 

 some experiments with a view to tracing out the nerve-supply 

 of the radial muscles. I have to thank Prof. Gotch for advice 

 as to the best way of stimulating the nerves, and Mr. G. W. 

 Smith for helping me to carry out the experiments. 



If in the limb-plexus the motor fibres of various segments 

 were crossed or mixed, and if, as some authors contend, the 

 radial muscles were polyneurous, we should expect to produce 

 a general, or at least an extensive, contraction of the fin- 

 muscles on the stimulation of one nerve. To test these views 

 experiments were made on the pectoral fin of Raja. Owing 

 to its great size, the muscles and nerves of this fin are 

 peculiarly well adapted for the purpose. 



The first series of experiments were made by directly 

 stimulating individual spinal nerves, and watching the con- 

 traction of the radial muscles. To insure definite and correct 

 results, the nerves were first severed near the spinal cord, and 

 were then stimulated in various ways at their proximal end, 

 the necessary precautions having been taken to keep the 

 tissues in good condition. The electric stimulus is the easiest 

 to use ; but a mechanical stimulus, applied either by snipping 

 the nerves with scissors, by ligaturing with a thread, or by 

 pinching with ivory forceps, gives, perhaps, the surest 

 result. 



It was found that the series of radial muscles of one side 

 could be made to contract regularly, in pairs, from before 

 backwards, by stimulating the successive nerves of the plexus, 

 beginning at the anterior end. Similarly the muscles contract 

 regularly in pairs from behind forwards on stimulating the 

 nerves in the reverse direction. It was determined with 

 absolute certainty that the stimulation of one nerve does 

 not produce a general contraction of the muscles of the fin, 

 but only of a limited portion of the musculature corresponding 

 in position to the nerve. 



Owing to the fact that the radial muscles lie very near 



