268 



THE NERVOUS SYSTEM 



the tuber culum olfactorium. According to Retzius, a small oval mass is present 

 in the anterior perforated substance of man immediately adjacent to the ol- 

 factory trigone, which represents this tubercle. 



Olfactory bulb 



Anterior commissure 

 Anterior perforated substance 

 -Amygdaloid nucleus 

 Pyriform area 



Fig. 199. Ventral view of a sheep's brain, pyriform area shaded and anterior commissure 



exposed. 



The Pyriform Area. The lateral olfactory gyrus is continuous at its caudal 

 extremity with the hippocampal gyrus (Figs. 197, 198), and the two together 

 form the pyriform area or lobe (Fig. 199). In the adult human brain it is more 

 difficult to demonstrate the continuity of these parts. As the temporal lobe is 



Hippocampal rudiment 



Corpus callosum -. 

 Septum pellucidum 



Fornix . 

 Anterior commissure. 



Paraterminal body ?^~ , -= 

 Hippocampal rudiment -.. 



Olfactory trigone , *"., 

 Olfactory tract ^^^^ 

 Olfactory bulb^ 



Intermediate olfactory stria'' 



Lateral olfactory gyrus and stria' 



t 



Anterior perforated substance 

 Limen insulce 



L Hippocampus (gyri 

 Andrea Retzii) 



-Fascia dentata 

 |T"-- Fimbria of hippocampus 



" Hippocampus (proper) 

 Hippocampus 

 ** Hippocampal gyrus 

 N - Cauda fascia dentata 

 Uncus 



Diagonal band 

 Fig. 200. Diagram of the rhinencephalon. 



thrust rostrally and the insula becomes depressed, the pyriform area is bent 

 on itself like a V (Fig. 198). The knee-like bend forms the limen insulce, and 

 with the rest of the insula becomes buried at the bottom of the lateral fissure. 

 The continuity of the pyriform area is not interrupted in the adult, though part 



