626 



THE NEKVOUS SYSTEM. 



In" the hippocampus impressions of smell are brought into relation with those of 

 other senses (probably taste) ; and from the hippocampal cells fibres are emitted 

 to form a system known as the fornix, which establishes connexions with the 

 hippocampus of the other hemisphere and with the hypothalamus, thalamus, and 

 more distant parts of the brain. 



The rudiment of the hippocampal formation that develops on the medial surface 

 begins in front, alongside the place where the stalk of the olfactory peduncle (which 

 becomes the trigonum olfactorium) is inserted ; it passes upwards to the superior 

 end of the lamina terminalis, from the rest of which it is separated by a triangular 

 mass of gray matter called the corpus paraterminale (Fig. 555) ; and then it proceeds 

 backwards, fringing the fissura chorioidea in the whole of its extent, ending below 

 in the temporal region alongside the posterior part of the area piriformis. The 

 anterior part of this great hippocampal fringe of the pallium does not attain its full 

 development in the human brain and remains as a more or less vestigial aborted 



Gyrus cinguli 

 Commissura fornicis j 

 Corpus fornicis 

 Corpus callosum 

 Septum pellucidum 

 Sulcus cinguli 



Sulcus cinguli 



Paracentral area 

 ! Paracentral sulcus 

 ' Sulcus centralis 



Gyrus frontalis superior 

 Lamina chorioidea 



Foramen 

 interventriculare 



Hippocampal rudiment 

 Incisura sulci cinguli 



Olfactory bulb ,. 

 Corpus paraterminale' / 

 Columna fornicis 



Olfactory tract 

 Stria olfactoria lateralis / 

 Nucleus amygdalae 



Piriform area 



Thalamus (cut surface) ', 



Rhinal fissure 

 Cauda fasciae dentatte 



'Sulcus praecunei 

 ., Praecuneus 



.. Sulcus subparietalis 



Fossa parieto- 

 -'occipitalis 



-Sulcus paramedu 

 Area striata 



.Sulcus 

 sagittalis ct 



.Sulcus 

 retrocalcari: 



Area striata 



\ \ Sulcus polaris inferior 

 \ \ Sulcus calcarinus 

 \ iSulcus sagittalis gyri linguali 

 \ Sulcus collaterals 

 , Hippocampus 



', , Splenium of corpus callosum 

 \ Fascia dentata 



, Crus fornicis 

 Gyrus paradentatus 



Hippocampus Fimbria 

 FIG. 554. MEDIAL ASPECT OF THE RIGHT CEREBRAL HEMISPHERE, WITH THE OLFACTORY PARTS COLOURED. 



structure ; but the posterior part undergoes a peculiar transformation. The tertiary 

 olfactory neurones, coming mainly from the posterior part of the area piriformis, enter 

 the. margin of the hippocampal formation, and the small cells which receive these 

 incoming fibres multiply rapidly during the third month, and arrange themselves 

 in a densely packed row of granules, which represent the distinctive feature of the 

 fascia dentata (Fig. 556). At first this cell-column is continuous at its peripheral 

 margin with a much more loosely packed column of larger and less numerous cells, 

 which represent the hippocampus ; and these in turn give place to the more 

 diffusely arranged and laminated cells of the typical cortex cerebri, which we 

 the neopallium. As development proceeds both the dentate and hippocam] 

 columns of cells rapidly increase in length, and both appear to push their w 

 towards the ventricle (Fig. 556, B) into the substance of the wall, which becom< 

 correspondingly thickened. The ventricular swelling thus formed is the hip 

 campus ; and it is important to recognise that this swelling is not produced 

 any invagination of the surface, such as is usually described under the name of tl 



