Development of Neopallium 109 



The brain of the South American mud-fish is 

 an example of the highest state of development 

 reached by this organ in bony fishes ; the pallial 

 formation of its hemispheres contains a fairly 

 compact layer of cortical nerve cells, its 

 lateral extremities show signs of commencing 

 specialisation to form the pyriform lobes into 

 which olfactory tracts penetrate, and its mesial 

 extremity forms what are known as rudimentary 

 hippocampal lobes. Beyond this the grey 

 superficial strata lining the basal ganglia con- 

 tain a layer of pyramidal cells (the epistriatum) ; 

 which receives terminal fibres from various sen- 

 sory organs, and passes into, and possibly 

 constitutes an important element in the develop- 

 ment of the neopallium. But the cortical struc- 

 tures of the highest orders of fishes, as well as 

 those of amphibians and reptiles, can only be 

 taken as indications of the first stage of the 

 labour attending the birth of a true neopallium, 

 such as that which exists in the cerebral hemi- 

 spheres of the Mammalia. 1 



We may now refer to the instinctive be- 



1 The Nervous System of Vertebrates, by Prof. J. B. Johnston, 

 pp. 255, 297, 310, Fig. 152. Also the Arris and Gale Lectures, 

 pp. 151-2, the Lancet, January 15, 1910. 



