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b'punded externally by the anterior end of the calcaririe fissure, and is associated 

 with the forward turn of the cingulum. 



The hippocampus is the name applied to the curved appearances produced in 

 the floor of the lateral ventricle by the peculiar foldings of this part of the cerebral 

 cortex. The kippocampal I/III-HX is the main gyrus of the teutori.-d surface of the, 

 liiubic lobe. Kxternally it is separated from the fu.-ifonn gyrus by the collateral 

 fissure, and it is bounded internally by the hippocampal or dentate fissure. Poste- 

 riorly it is partially dividud by t he calcarine fissure into the lingual gyrus (of t he tempo- 

 ral lobe) and the isthmus of the gyrus foruicatus. Its anterior extremity is hooked 

 backwards and is known as the uncus. This is almost entirely separated from the 

 temporal lobe by a groove, the temporal notch. If t lie hippocampal fissure be opened 

 up, the dentate fascia or gyrus and the /imhriti will be M'CU. These lie side by side, 

 separated by the shallow hmbrio-dentate sulcus. The free edge of the dentate 

 syrus presents a peculiarly notched appearance, produced by numerous parallel 

 grooves cutting it transversely. Its posterior end, sometimes called the fasciolu 

 cint ri. continues backwards over the splenium of the corpus callosum. and upon the 

 upper surface of the corpus callosum appears as a thin strip of grey substance which 

 contains embedded in it the medial and lateral longitudinal strip. This thin strip 

 is sometimes called the supracallosal gyms, and is thought to represent a vestigial 

 part of the hippocampal gyrus. The fimbria is but the finibriated, free border of the 

 posterior or end of origin of the fornix, so folded as to project into the hippocampal 

 fissure, parallel with the dentate fascia. It is a conspicuous band composed almost 

 entirely of white substance, continuous laterally with the thick stratum covering 

 the ventricular surface of the hippocampus. It begins anteriorly in the hook or 

 recurved extremity of the uncus. Traced backwards, it is seen to curve upwards, and 

 within the ventricle it becomes part of the general accumulation of the white sub- 

 stance (alrcus) of the surface of the hippocampus, which accumulation is the be- 

 ginning of the fornix. The free border of the fimbria (seen in section) is known as 

 the tun in fimbria;. The fimbria is separated from the cerebral peduncles by the 

 chorioid fissure, the thin, non-nervous floor of which alone intervenes between the 

 exterior of the brain and the cavity of the lateral ventricle. 



The hippocampal fissure attains its greatest depth between the dentate fascia and 

 the hippoeampal gyrus, and the resulting eminence produced in the floor of the lateral 

 ventricle is known as the hippocampus major, as distinguished from the lesser 

 eminence produced posteriorly by the end of the calcarine fissure and known as the 

 hi/ipommpus minor (calcar avis). The collateral fissure may likewise produce a 

 bulging in the wall of the ventricle, the collateral eminence. In transverse sections of 

 the hippocampus major, the layers of grey and white substance present a coiled ap- 

 pearance known as the cornu ammonis. Externally the medial surface of the 

 hippocampal gyrus adjoining the dentate fascia has reflected over it a delicate re- 

 ticular layer of white substance known as the substantial nticuluris <ilbu (ArnoUii). 



The fornix is the great association "pathway of the limbic lobe, and is largely 

 concerned in the apparatus of the rhinencephalon. It is a bilateral structure arched 

 beneath the corpus callosum, with which it is connected anteriorly by the septum 

 pellucidum. Posteriorly it passes in contact with the splenium. It consists of two 

 prominent strips of white substance, one for each hemisphere, the ends of which are 

 separate from each other, while their intermediate parts are fused across the mid-line. 

 These run above the tela ehorioidea of the third ventricle, and their lateral edges 

 (tamia fornicis) rest, on each side, along the line of the taenia ehorioidea. The 

 posterior, separate ends are known as the posterior pillars or erura of the fornix: the 

 fused, intermediate portion is the body, and the separate, anterior ends are the an- 

 terior pillars or columns of the fornix. 



The posterior pillars or crura of the fornix.- When seen from the medial 

 aspect of the hemisphere, the fused portion of the fornix, in the separation of the 

 hemispheres, is split along the mid-line (fig. 619). The half under examination may 

 lie seen to course obliquely outwards under the splenium of the corpus callosum, 

 and then, continuous with the fimbria, to curve forwards and downwards towards 

 the uncus. The greater mass of the fibres cotirsinir in the fornix arise as out irrowths 

 of the cells of the uncus, hippocampal gyrus, and dentate fascia. They accumulate as 

 a dense stratum on the ventricular surface of these gyri. termed the alveus, which 

 crops out wards as the fimbria and which passes backwards and upwards: upon reach- 

 ing the region of the splenium it turns obliquely forwards under it and approaches the 



