930 



THE XER VE SYSTEM 



CENTRAL OR CORTICAL PARTS OF THE RHINENCEPHALOX. Following the sug- 

 gestion made by Broca in 1878, it has been customary to designate these various 

 parts by the comprehensive term limbic lobe. Broca's notion of the limbic 

 lobe in man was founded upon attempts to homologize the human cerebral con- 

 fio-urations with those found in lower animals. More recent researches have 

 proved that Broca's "limbic lobe" included parts belonging to the neopallium and 

 not to the rhinencephalon. The term is therefore inappropriate in a morphologic 



sense. 



The hippocampus is the submerged, peculiarly folded margin of the cerebral 

 hemisphere produced by the hippocampal fissure. Its architecture can best 

 be understood by referring to a frontal section (Fig. 682). It is seen that the 

 whole cerebral marginal wall is pushed into the ventricular cavity (middle cornuj 

 as a fold caused by the intrusion of the hippocampal fissure. A secondary 

 fold not produced by a fissure, however constitutes the gyms dentatus. Super- 

 imposed lies a prominent white band the fimbria composed of axones from 



INDUSIUM AND STRlJE 



SUBCALLOSAL GYRE 

 AREA PAROLFACTORIA 



MEDIAL STRIA 



FUSION OF FASCIOLA 

 CINEREA AND DEN- 

 TATE GYRE 



GYRI OF ANDREW 

 RETZII 



FASCIOLA CINEREA 



DENTATE GYRE 

 HIPPOCAMPAL FISSURE 



ICUS 



FRENULUM GIACOMINI 

 CYRUS SEMILUNARIS 



CYRUS AMBIENS 



FIG. 681. Schematic representation of the rhinencephalon, mesal aspect. 



the hippocampal cells, assisting in the formation of a white lamina, subjacent 

 to the ependyma of the ventricle, and called the alveus. The whole formation 

 is characteristic of this region, and from its fancied resemblance to a ram's horn 

 a symbol used on the temple of Jupiter Ammon the name of cornu ammonis 1 

 has been given; the name hippocampus was applied because of a fancied resem- 

 blance to the marine animal of the same name. The ventricular relations and 

 internal structure of the hippocampus will be given farther- on (p. 943). 



The uncus, with the atrophied lateral olfactory stria, is all that remains in the 

 human brain of the relatively large pyriform lobe of lower forms. It appears 

 to be a hook-like retroflexion of the hippocampal gyre which is partially encircled 

 by the gyrus dentatus. Morphologically speaking, it is only the apical portion, 

 or that which lies caudad of the dentate gyre which is the true uncus (the gyrus 

 intralimbicus of Retzius); the remainder is neopallial and a part of the hippo- 

 campal gyre. The uncinate or intralimbic gyre may be traced caudad in the 



'Frequently, but incorrectly, given as Amman's Horn. 



