Section VII. 

 The Intshbrai'J. 



The research of Edingsr, Das Zwisahenhifn, ('98), presents 

 an account of tne fibre-tracts of the interbrain of Selachii 

 and Amphibia as ienaonstratel by the Wei^ert method. It remains 

 for lie to add to the results of that »?ork a description of the 

 morphology of the neurones proper to the interbrain of Mustelus 



1. The Thalamus. 

 The thalami of a selachian are so small in proportion 

 to the other parts of the brain (Pig.l.th.) that certain of 

 the older anatomists were thereby caused to overlook the inter- 

 brain entirely; see Section II. The small size of the thal- 

 amus is, I find, the expression of a low degree of organiza- 

 tion. Several investigations have made it clear that the thal- 

 amus of a mammal has several well-defined thalamic nuclei. Tne 

 thalamus of Mustelus, however, has remained in a condition of 

 such primitive simplicity that it is not practicable to insti- 

 tute very strict comparisons between its neurones and those 

 which are characteristic of higher forms. Before such compar- 

 isons can be of much value, a study must be made of thalami 



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