112 PHYSIOLOGICAL SERIES. 



with the hippocampus of the mammalian brain (figs. 31, 32, 

 & 33). This hippocampal formation also extends beyond the 

 dorso-mesial edge of the hemisphere, and forms in different 

 reptiles and ln'nls a variable area of the dorsal surface (see 

 "Further Observations on the Fornix," Journ. Anat. & Phys. 

 vol. xxxii. p. 245). 



The hippocampal formation presents a very different appear- 

 ance to its mammalian homologue because that peculiar modifi- 

 cation of the edge of the hippocampus which in Mammals 

 produces the fascia dentata, has not yet occurred in the 

 Sauropsida, although in many Saiiria the first stage in the 

 development of the fa-cia dentata, viz., a formation of numerous 

 > i nail cells at the ventral edge of the flat hippocampal plate, is 

 distinctly recognizable. 



Two simple rounded commissures are placed close together in 

 the lamina terminalis. The dorsal of these represents the 

 p.-alterium of Mammals, being derived from the hippocampus. 

 In many Reptiles such as Sphenodon and the Lacertilia, the 

 caudal half of this commissure is separated from the rest and 

 crosses the middle line not in the lamina terminalis but in a fold 

 <>f the roof between the paraphysis and dorsal sac. This "com- 

 mi-Miru aberrans hippocampi " (usually known by the misleading 

 title "oommiMim pallii posterior ") is probably a modified in- 

 heritance from the Amphibia, in which certain fibres from the 

 caudal part of the cerebral hemisphere cross the mesial plane 

 along with the fibres of the superior commissure (commissnra 

 habenulse). 



That part of the pallium which forms the bulk of the whole 

 nervou- -y-n-m in Mammals is represented in Reptiles by a 

 -mall insignificant area on the dorso-lateral aspect of the 

 bamilphere, which is not sharply differentiated from the pvri- 

 tonn lobe below it. The n.-o pallium (a- 1 have called this pan 

 of the pallium [Journ. Anat. & Phys. vol. xxxv. 1901, p. 431]) 

 is so poorly developed that the fibre-systems to which it gives 

 rise internal capsule, pes pedunculi, and pyramidal system, are 

 absent in the reptilian brain. The chief cerebral tracts are in 

 connection with the olfactory centres, and include some between 

 the olfactory areas and the Uppooamptl cortex that are of 

 special importance, as they are the first cortico-sensory connec- 

 tions to appear in the Vertebrate series. 



