334 BRAIN MECHANISMS AND LEARNING 



which gives a collateral branch to the sphincter fibre and a collateral branch to 

 radiatory fibres. I will provide you with the reprint of the paper I published on this 

 subject. 



EccLES. I am very interested in the physiological significance of these histo- 

 logical findings. If the same nerve fibres do innervate these two different muscles of 

 the iris they might still do it by the same chemical transmitter which could work in 

 opposite ways on two muscles. It depends on the operation of the respective 

 receptive sites on the muscles. For example we know that acetyl-choline can work 

 on cardiac muscle inhibiting it and on skeletal muscle exciting it. We certainly 

 need a functional and pharmacological investigation of neurones concerned in 

 transmission to these iris muscles. 



