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of the optic lobes, the horizontal section of which is triangu- 

 lar in the opposite sense to that of the hemispheres. 



The base (ventral surface) of the hemispheres exhibits a 

 slight protuberance in the latero-caudad portion, which is 

 due to the protrusion of the occipito-basal Iohc.{^) The latter 

 is not a subdivision of the cortex, but a well-defined por- 

 tion of the axial lobe, in the sense elsewhere employed. 

 This lobe can probably be distinguished in all Sauropsida. 

 It is partially separated from the remainder of the axial lobe 

 by a fibre tract, and bears laterad and dorsad a film of cor- 

 tex which projects caudad as a free occipital lobe of cortex 

 for a short distance and terminates in a velum cerebri. The 

 latter is morphologically a part of the wall of the lateral 

 ventricle, which has here lost its cellular elements and con- 

 tains at one point the taenia thalami. 



The extent to which this lobe is developed varies greatly 

 even in reptiles. It is reduced to a minimum in birds. It 

 contains the undoubted homologue of the hippocampus, but 

 in the black-snake that portion homologous with the hippo- 

 campus is relatively highly diff'erentiated. Even the por- 

 tions corresponding in cellular structure to the fornicate and 

 uncinate gyri may be distinguished, though there is, of 

 course, no external indication of this distinction. The 

 terminal, caudad portion (homologue of the uncinate gyrus) . 

 contains densely packed fusiform cells of relatively small 

 size, while, near the juncture of the free portion with the 

 axial lobe laterad, there is a larger area containing much 

 larger cells of the same type, which corresponds with the 

 fornicate gyrus of mammals (Plate X, Fig. 6). At some 

 levels a deep depression separates the hippocampus from the 

 remainder of the cortex. 



Ventrally the occipito-basal lobe is set oft' from the axial 

 lobe proper b}- the pyramidal tracts, and is filled with small 



I The use of the word "lobe" in this and subsequent cases is a pure convention, 

 from which no escape could be found. " Region " might be a preferable term, if not too 



