498 J. B. JOHNSTON 



Fig. 10 Section through the anterior commissure. Although the hiteral ol- 

 factory area is continuous in these sections and even the nucleus caudatus is 

 nowhere wholly separated from it, one can clearly see the beginnings of the 

 segregation of the pyriform lobe, diagonal band and caudate nucleus by reason 

 of the enlargement of the lateral forebrain bundle (cms). This process will be 

 completed in later stages by the development of the lentiform nucleus and the 

 further enlargement of the crus. 



Fig. 11 Section just rostral to the preoptic recess where the diagonal band 

 turns up in the medial wall. The dark mass on the medial surface of the area 

 parolfactoria represents the beginning of the nucleus of the diagonal band, 

 which corresponds to the gyrus subcallosus of the mammalian brain. The 

 nucleus caudatus is connected beneath the ventricle with the area parolfactoria. 

 From this level rostrad the olfactory area or lobe is quite continuous from its 

 lateral border at l.pyr. to its medial border near fi. 



Fig. 12 Section 60 microns rostral to figure 11, where the diagonal band fibers 

 rise up in the medial wall to join the fimbria. Although the cells of the pyri- 

 form lobe and pallium lie immediately in contact, there appears in many sec- 

 tions a very sharp line as if it were caused by a delicate septum running dorsad 

 from the small fiber bundle beneath l.pyr. 



Fig. 13 Section through the tuberculum olfactorium. Note that the ventral 

 ventricular sulcus here descends nearer to the surface than elsewhere so that 

 the somewhat bulging tuberculum contains a large pouch of the ventricle. 



Fig. 14 Section through the olfactory peduncle. The ventral part of the 

 section cuts the rostral wall of the tuberculum while its dorsal part cuts the 

 olfactory formation. 



