SEPTUM, HIPPOCAMPUS, PALLIAL COMMISSURES 419 



fovea limbica medialis, or sulcus rhinalis medialis. Since the 

 term sulcus rhinalis (lateralis) is used for the sulcus which marks 

 the boundary between the pallium and the olfactory area laterally, 

 the term sulcus rhinalis medialis seems peculiarly appropriate 

 for this sulcus in the medial wall. In other words, the writer 

 having used the term sulcus limitans hippocampi throughout this 

 paper in the same sense as in former papers, would now sub- 

 stitute for it the term sulcus rhinalis medialis. The term sulcus 

 limitans hippocampi of Elliot Smith is synonymous with the 

 term sulcus fimbrio-dentatus. 



As for the term primordium hippocampi, the writer believes 

 that it is best to retain this to include the equivalent of hippo- 

 campal formation plus septum pellucidum. Two considerations 

 strongly support this. The one is that the two are undivided and 

 indistinguishable in fishes, the other is that the fimbria is usually 

 considered to be an integral part of the hippocampal formation 

 but is separated from Elliot Smith's primordium hippocampi by 

 his sulcus limitans. 



8. The hippocampal commissure and corpus callosum corre- 

 spond in all their morphological relations to the two commissures 

 in the roof of the telencephalon in selachians which are related 

 respectively to the primordium hippocampi and the somatic sen- 

 sory area. The marsupial Didelphys possesses true corpus cal- 

 losum fibers running in the dorsal forebrain commissure. This 

 is apparently the typical condition in selachians, marsupials and 

 mammals. A corpus callosum has not been certainly demon- 

 strated in reptiles. 



9. The development by Elliot Smith of the idea that the pallial 

 commissures are originally imbedded in the sub-pallial parater- 

 minal body and that the great development and arching up of the 

 corpus callosum has stretched and raised up the paraterminal 

 body to form the septum pellucidum, has led to the recognition 

 of a large body situated above the foramen of Monro which, 

 although apparently in a pallial position, has had a sub-pallial 

 origin. This is the body known in the work of recent writers 

 as the supraforaminal portion of the paraterminal body. This 

 body in lizards not only forms a bed for the anterior pallial com- 



