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J. B. JOHNSTON 



Fig. 84 Diagram of the forebrain of Scyllium to illustrate the author's con- 

 ception of the relations. The hippocampal primordium is separated from the 

 paraterminal body by the neuroporic recess. This primordium gives rise to two 

 structures in higher vertebrates: hippocampal formation and a residual body 

 less highly organized which is represented in mammals by the septum pellucidum. 

 This residual structure is represented in the following diagrams by the flecked 

 or spotted area. 



Fig. 85 Diagram of the brain of the turtle to illustrate the view set forth in 

 this paper. Not only in the turtle but in lizards and other reptiles the body 

 which rims along over the foramen, between it and the hippocampal cortex, is 

 hippocampal primordium. 



