202 



are summed up in these words: — "So wurde es höchst wahrschein- 

 lich, daß der hinter dem Riechlappen liegende Lobus parolfactorius der 

 Reptilien und Vögel ein Hirnzentrum ist, das in Beziehung steht zu 

 peripher vom Trigeminus innervierten Gebilden, daß wir hier vielleicht 

 ein Hirnzentrum für die Zungen- und Kaubewegungen haben" (p. 155). 



Turning to the consideration of the mammalian brain Edinger 

 states that no one has ever traced a single olfactory fibre into the 

 tuberculum, although the latter has hitherto been universally considered 

 as part of the smell-apparatus (p. 155). But if the Lobus parolfac- 

 torius [i. e. the tuberculum olfactorium] of mammals has no connection 

 with the olfactory tracts and if it be considered in the highest degree 

 probable that it has connections with the pons Varolii analogous 

 to the similarly situated part of the brain in birds, where the beak, 

 and in reptiles, where the tongue, is the principal means of obtaining 

 food, then the question arises whether the so-called tuberculum olfac- 

 torium in the mammal is not the centre for similar orally-related 

 functions (p. 156). 



To test the validity of this hypothesis Edinger states that he 

 examined a large number of mammalian brains and found that the 

 tuberculum olfactorium was highly developed in those animals in: which 

 the snout plays a special part as an organ of sense and particularly 

 in those provided with special tactile hairs and sense-organs (p. 156). 

 Finally he concludes that the tuberculum olfactorium varies in size 

 with the development of the sensitiveness of the snout and of the 

 fifth cranial nerve, which innervates the latter, and that the tuberculum 

 olfactorium is the cerebral centre for impressions coming from the 

 skin of the snout. • 



Edinger's novel suggestion as to the functions of the tuberculum 

 olfactorium, which has been briefly summarised in the preceding para- 

 graphs, receives no confirmation from my observations. During the 

 last fourteen years I have repeatedly called attention to the fact that 

 the size of the cortex of the tuberculum olfactorium varies directly 

 with that of the olfactory bulb (see Edinger's own Fig. 3 in confirmation 

 of this!) and that when the olfactory bulb disappears, as in the 

 Odontoceti, the cortex tuberculi becomes almost completely atrophied. 



There are two closely-related mammals which provide an ideally 

 crucial test of the fallacy of Edinger's theory. I refer to the two 

 Monotreme genera, Ornithorhynchus and Echidna, the reference to 

 which is particularly apposite in this connection, seeing that Edinger 

 has included them both in the five mammals selected for representation 

 with the remark "die Tiere mit langen Schnauzen haben alle einen 

 mächtigen Lobus parolfactorius" (Fig. 4, p. 158). 



