140 



PHYSIOLOGICAL SERIES. 



is seen to extend on to the mesial surface of the hemisphere, 

 where it expands to form a pyriform tubercle, which is 

 placed immediately below the "tail" of the hippocampus 

 (fascia dentata). The pyriform lobe is separated from tin- 

 rest of the "pallium" by an exceptionally deep rhinal fissure, 

 which is seen in the specimen (fig. 35) as a mere line upon 

 the ventral surface. 



To the mesial side of the anterior half of the pyriform 

 lobe there is a deep endorhinal fissure separating it from 



Fig. 36. (Nat. size.) 



FASC.DENT. 



OLF. BULB 



COMM.V. 



PXR. L. 



Fig. 37. (Nat. size.) 



3 



-OLF. BULB. 



V.CEKEB.MAG. 



CER.HEM. 



-FLOC. 



CER 



an elliptical projection of peculiar cortex, commonly known 

 as the tubereulum olfactorium. The presence of a definite 

 cndorliinal fissure is peculiar to the Monotremes; in other 

 mammals there is merely a shallow furrow in the i-orre- 

 -ponding situation lodging the compact (external) olfactory 

 tract. In the Monotremes there is no such compact trad, 

 because the fibres which proceed from the olfactory bulb 

 to the pyriform lobe are scattered diffusely over the surface 

 of the latter. 



In comparison with the brains of most other mammals it 

 will be found that these regions of the brain olfactory 

 bulb, olfactory tubercle, and pyriform lobe are relatively 



