102 ILLINOIS STATE ACADEMY OF SCIENCE 



fissures — the hippocampus fissure (fs. hip.), where it 

 meets the hippocampus, and the rhinal fissure (fs. rh.) 

 where it meets the pyriform cortex (lob. p.) 



Ventrally (Fig. 3) also these two olfactory cortices, 

 lateral and medial, are separated by another wedgelike 

 mass composed of two structures, one behind the other, 

 both enormously developed in this brain. The anterior 

 one is the great rounded olfactory tubercle (tub. ol.), 

 lying just behind the huge olfactory bulb (b. ol.). It is 

 encircled by a deep fissure, whose lateral portion is called 

 the endorhinal fissure (fs. erh.). This is an important 

 landmark and will be referred to later. The posterior 

 of the two structures is the enormous amygdaloid com- 

 plex (amg.). It lies just behind the olfactory tubercle 

 and fills the rest of the basal surface ,of the brain. 



Both these structures are complex as well as very 

 large. In microscopic sections the olfactory tubercle 

 presents a highly spectacular picture of convoluted and 

 rolled cell masses or sheets, composed of cells of many 

 sizes and types — the so-called ''islands of Calleja". The 

 olfactory tubercle receives great numbers of secondary 

 olfactory fibres from both the lateral and median olfac- 

 tory tracts, and emits a" great quantity of tertiary fibres 

 which join those from the pyriform lobe and sweep be- 

 neath the ventricle in a broad stream up into the median 

 wall of the hemisphere to make connections with the 

 hippocampus. 



The amygdaloid complex (amg.), whose enormous su- 

 perficial extent has already been emphasized, exceeds 

 internally this area both in breadth and length (Fig. 3, 

 dotted outline). It consists of five distinct nuclei and 

 perhaps more subsidiary ones. The anterior ones are 

 in continuity with the cell bed of the stria terminalis, 

 the great complex fibre stream which connects the amyg- 

 daloid region with other parts of the brain. The poster- 

 ior lateral ones are in part continuous with the lower 

 edge of the pyriform cortex, from which they appear to 

 have been derived along a line of infolding whose ex- 

 ternal manifestation Dr. Johnston has called the amyg- 

 daloid fissure. This fissure, externally very obscure but 

 internally obvious, continues the endorhinal fissure (fs. 



