53 



fibres, the olfactory lobe (possibly the bulb?) is intimately connected 

 with lower parts of the nervous system. Edinger suggested that 

 some of them enter the fillet. In Perameles the great majority 

 of them enter the pes pedunculi and are possibly reflex fibres. A few 

 however seem to end in the mammillary region of the floor of the 

 third ventricle. 



All the various parts of the smell centre are connected with the 

 pallium by association bundles, but one is not justified in considering 

 the regions of the pallium so connected as parts of the olfactory centre. 

 Thus the tuberculum olfactorium is closely connected with the anterior 

 part of the pallium by a strong bundle. From its connections it is 

 apparently homologous with the anterior segment of the cingulum of 

 Beevor — but quite distinct from the cingulum proper. 



There seems to be no legitimate reason for including the callosal 

 gyrus in the limbic lobe, such as Broca, extending the views of Foville 

 and Gerdy, has done. The brain of the non- placental Mammal shows 

 that the callosal gyrus is not „limbic"; and there is no reason to 

 connect it with the olfactory sense, apart from the presence of associat- 

 ing fibres to the olfactory centre proper. The true limbic lobe (the 

 Sauropsidan cerebrum is probably purely „limbic") consists in a typical 

 early (i. e. unbent) Mammalian cerebrum of a dorsal (hippocampal) arc 

 and a ventral (pyriform) arc united in front by the precommissural 

 area and the tuberculum olfactorium. In Eutheria, the anterior part 

 of the hippocampus becomes atrophied to form the supracallosal gyrus 

 of Zuckerkandl (induseum griseum and striae Lancisi). The original 

 ventral limb becomes bent and the bending of the hippocampus brings 

 its posterior part into a ventral position. 



All such fornix as exists in the Metatherian brain, either arises 

 or ends in the hippocampus. Since the hippocampus is coextensive 

 with the lateral ventricle, its anterior extremity lies in front of the 

 lamina terminalis and the anterior fibres of the fornix system 

 proceed to their destination directly, so that their connections are 

 readily determined. The fibres which are leaving or about to 

 enter the hippocampus, cover its ventricular aspect forming the al- 

 veus. The alveus fibres from the descending limb of the hippo- 

 campus collect to form the fimbria (Fig. 1 fi) — in Ornithorhyn- 

 c h y u s as there is practically no descending limb, there is practically 

 no fimbria — which runs forwards to the ventral aspect of the "septum 

 lucidum" (s). The fibres from the anterior or dorsal part of the hippo- 

 campus collect at the dorsal margin of the "septum". From each of 

 these parts of the fornix commissural fibres pass across in the thickened 



