532 



ments of the body, as my colleague Prof. W. H. Wilson, has demon- 

 strated, and the hippocampus by means of the fornix is brought into 

 more intimate relationship with the thalam- and mesencephalon than 

 any other part of the "smell-brain". 



In the Mammalia, while the hippocampus maintains its important 

 role, the pyriform lobe becomes especially well - developed, probably 

 because it aÖ'ords the only path for smell-impressions to the neopallium, 

 which now becomes the dominant organ of the nervous system. 



Let us now leave these speculations and return to the examination 

 of the corpus paraterminale. 



It has already been seen that the paraterminal body begins near 

 the dorso-medial corner of the cerebral hemisphere, where the mesial 



edge of the hippocampus 

 is situated, and extends 

 downward to form part 

 of the mesial wall (Fig. 1). 

 It has also been shown 

 that the tuberculum ol- 

 factorium extends around 

 the ventro-mesial corner 

 to form part of the mesial 

 surface. Where do these 

 two constituent elements 

 of the mesial wall meet 

 — is it at 5 or at O 

 (Fig. 1)? 



To decide this question 

 and at the same time to 

 establish the identity of 

 the paraterminal body 

 beyond all doubt let us 

 study some more sections. 

 I have chosen a series 

 of coronal sections of a larval Lepidosiren of the same stage of develop- 

 ment as those represented in Figures 9, 10 and 11, because the ventral 

 bulging of the tuberculum olfactorium is not so extensive as it is in 

 the adult: hence these sections are less unlike those of other verte- - 

 brates than those of the adult. ^ 



Starting with the examination of Fig. 12, in which the formatio j 

 bulbaris is seen as a cap on the dorsal aspect of the hemisphere, 

 the whole mesial wall is obviously composed of paraterminal body. ! 



Fig. 12. Coronal section of a larval Lepidosiren 

 (stage 38), passing through the olfactory bulbs, which 

 form dorsal caps on the hemispheres. Series 140 A. 

 Section 16. 3. 4. 



