384 J. B. JOHNSTON 



In figures 14 and 17 are shown two transverse sections of the 

 telencephalon of the hinge turtle (Cistudo Carolina), one near 

 the olfactory peduncle and one near the interventricular fora- 

 men. In the section near the foramen the locus of the recessus 

 neuroporicus is indicated by the position of the anterior com- 

 missure. If we compare in the turtle and the selachian that 

 portion of the hemisphere which lies dorsal to the level of the 

 neuroporic recess, we must recognize a differentiation of this 

 region in, the reptile's brain into two parts. The dorsal portion 

 is the hippocampal formation and is bounded by the sulcus limi- 

 tans of Elliot Smith ('03), s.f-d. in the figure. The remainder of 

 the area would be regarded as a remnant of the primordium 

 hippocampi of selachians in which differentiation of cortex has 

 not taken place. Within this primordium are found the com- 

 missura hippocampi and the upper part of the fornix columns, ■ 

 as is the case in selachians. In the lateral ventricle a groove is 

 seen at the level of the foramen which would be considered as 

 the ventricular boundary of this primordium hippocampi. The 

 body which we are thus hypothetically calling primordium hip- 

 pocampi is of course the same that has been compared by Meyer 

 ('92) and Unger ('06) with the septum pellucidum of mammals. 



As the transverse sections are followed forward this thicken- 

 ing continues but the appearance of distinctness between it and 

 the paraterminal body below gradually disappears. Deferring 

 comment on sections in this intermediate area we may pass to 

 the examination of figure 14. The section is taken behind the 

 olfactory peduncle. The hippocampal formation is clearly marked 

 in the medio-dorsal wall. The cortical layer stops suddenly and 

 a small portion of the medial wall is composed of small cells 

 without regular arrangement. This was called by Meyer part 

 of the septum pellucidum. Below this is a thickening projecting 

 into the lateral ventricle, apparently the same one as was seen 

 near the foramen interventriculare. There can be no doubt of 

 the interpretation of these three portions of the medial wall. 

 The lowest is directly continuous with the tuberculum olfacto- 

 rium below and receives olfactory tract fibers. It belongs to the 

 area parolfactoria and paraterminal complex. The uppermost 



