4 STUDIES ON THE CENTRAL NERVOUS SYSTEM 



opinion was contested by several anatomists and much 

 work had to be done before the correctness of Newton^s 

 theory was proved. This once more demonstrates that a 

 good theory often anticipates the facts. It depends only on 

 the nature of the theory or, perhaps more correctly, on the 

 quality of the brain, from which the theory issues. 



What is the reason why the optic nerves in higher animals, 

 and in men, only partly cross? This depends on the posi- 

 tion of the eyes in the head. The more frontal they are the 

 more non-crossing fibres are present. Cats and dogs, for 

 example, belong to the same class in the scale of evolution. 

 In dogs the eyes stand more laterally than in cats. Experi- 

 mental-anatomical study has proved that the number of 

 non-crossing fibres in cats is larger than in dogs. 



There is still another difference in the ascending scale. 

 I mean the development of the macula. We all know that 

 man has a very finely organized macula. It is by this spot 

 in the retina we can see very distinctly. A similar spot is 

 also present in monkeys but not in rabbits and is absent in 

 by far the largest number of vertebrates. It is also found in 

 some animals whose sight is highly developed, for example, 

 in many birds. 



The optic fibres terminate in two primary optic stations 

 in the brain, the external geniculate body and the corpus 

 quadrigeminum anticum. It is often asserted that there 

 is still a third primary station, the pulvinar. Later on I 

 shall return to this point. 



Fibres proceeding to the geniculate body conduct the 

 stimuli by which conscious sight is made possible. They 

 are spread throughout the geniculate body, where the 

 second optic neuron begins. Its cells send their fibres by a 

 long tract to the cortical optic centre, lying in the occipital 

 lobe. The other optic fibres, proceeding to the midbrain, 

 conduct stimuli, which may cause reflex movements of the 

 eye muscles and of the pupils. 



For many years there have been two lines of thought as 



