ICO PHYSIOLOGICAL SERI 1 



The fascia dentata (like the hippocampal fissure which 

 marks its peripheral boundary) proceeds upward and 

 forward alongside the fimbriaas far as the dorsal commissure; 

 and then it passes forward above the dorsal commissure and 

 appears to lose itself in the precommissural area immediately 

 above the attachment of the olfactory peduncle. In a 

 t'resh brain (or by means of histological examination) the 

 fa-cia dentata may be traced forward practically into 

 continuity with the olfactory peduncle (Trans. Linn. Soc., 

 Zool. ser. 2, vol. vii. 1897, pi. 15. fig. 8). The hippocampal 

 fissure accompanies the fascia dentata in the greater part 

 of its course, but stops just as it approaches the neighbour- 

 hood of the olfactory peduncle. The mesial surface of the 

 olfactory peduncle passes backward into direct continuity 

 with the precommissural area, which is separated above by 

 the fascia dentata from the neopallium. This precommissural 

 area is continuous below with the tuberculum olfactorium. 

 and is bounded posteriorly by the lamina terminalis 

 containing the dorsal and ventral commissures. 



The retention in an undisturbed state of the cephalic 

 portions of this hippocampal formation is the most interesting 

 :ire in the brain of the Marsupial. In this it agrees 

 with the Monotreme, but is the more instructive because 

 the caudal parts of the hippocampus in the Marsupial have 

 assumed the configuration which is met with in other 

 mammals. 



The cephalic parts of the hippocampal formation are 

 retained in the Marsupial because the dorsal commissure is 

 derived from the hippocampus, and the great non-hippo* 

 cam pal commissure (corpus callosum) has not yet made its 

 appearance to disturb the integrity of the hippocampal arc. 



It is the ahsence of the corpus callosum and the retention 

 .f the supracommissural and precommissural parts of the 

 hippocampus undisturbed that renders the cerebral hemi- 

 >phere in the Monotremata and Marsupialia so inslni-'iive 

 to the student of the higher mammalian brains. For the 

 corpus callosum consists of a series of fibres at first 

 intermingled with those of the dorsal or hippocampd 

 commi.-sun-. but distinguished from them by the fact that 

 they come from a cortical area (the neopallium) other than 



