646 



but by differences in form and connections. They probably represent 

 the beginning of the true cortex cerebri. 



The pars dorso-lateralis is the primordium of the mammalian 

 pyriform lobe (uncus of man). The two dorsal parts constitute the 

 pars pallialis hemisphaerii (Gaupp) and are separated from the ventral 

 or sub-pallial parts by the zona limitans lateralis (B) and the zona 

 limitans medialis (D - F), these zones being clearly defined bands devoid 

 of nuclei. In the frog they mark also the positions of total fissures, 

 respectively the fissura endo-rhinalis (Turner) and the fissura limitans 

 hippocampi (Elliot Smith). Both dorsal parts receive secondary 

 olfactory fibers from the olfactory bulb, the medial part in small 

 numbers, the lateral part in large numbers. They are connected with 

 each other dorsally by association fibers. The dorso-medial part has 

 ascending and descending connections with the hypothalamus by way 

 of the medial forebrain tract. The dorso-lateral part has ascending 

 and descending connections with the thalamus by way of the lateral 

 forebrain tract. The medial and lateral tracts together constitute the 

 basal forebrain tract of authors. 



The pars ventro-medialis includes the primordia of the septum, 

 precommissural body and tuberculum olfactorium. It is directly con- 

 tinuous behind with the nucleus preopticus and hypothalamus. The 

 median forebrain tract (of very complex composition) extends throughout 

 this whole system from the olfactory bulb to the hypothalamus and 

 determines its morphological character. 



The pars ventro-lateralis is directly continuous with the ventral 

 part of the thalamus. It is characterized by the complex lateral 

 forebrain tract and contains the primordia of the mammalian corpus 

 striatum, though this structure is not differentiated as such in the 

 Amphibia. It receives large numbers of ascending fibers from the 

 thalamus and is chiefly concerned with non-olfactory correlations. 



All parts of the amphibian hemisphere are connected with the 

 epithalamus by way of the stria medullaris, though the nucleus pre- 

 opticus is the chief source of these fibers. Each of the four parts of 

 the hemisphere likewise receives secondary olfactory fibers. The efferent 

 olfactory impulses leave the hemisphere by two chief pathways: l)for 

 olfacto- visceral responses by way of the medial forebrain tract and hypo- 

 thalamus ; 2) for olfacto-somatic responses by way of the stria medullaris 

 and epithalamus. 



In the urodeles the zona limitans medialis (Fig. 1 D-V) is as 

 clearly defined as in anurans, but the other landmarks of the hemi- 

 sphere are not so obvious as in the frog, due chiefly to the imperfect 



