THE CEKEBEUM OE PBOSENCEPHALON. 



177 



picted in the pigeon two of these bundles which are for the purpose of con- 

 necting the frontal with the occipital segment of the mantle. The dorsal 

 one passes close beneath the cortex, while the ventral one passes over the 

 surface of the mantle, just like the fibers of the layer of cortical association 

 (see also Fig. 83). 



The mantle of birds is, so far as we now know, not much more extended 

 than that of reptiles. Only in the frontal portions, and then in the occipital 

 lobe, — appearing here for the first time, — does it manifest any essential 

 progress. 



In order that you may quite clearly recognize the development of the 

 brain-mantle, — the increase of the cortical area, — I present in Fig. 133 a 

 reptilian brain which I have inscribed within the brain of one of the lowest 



Fig. 122. — :Sagitta,l section through the brain of an adult ray. 



mammals: a marsupial. The reptilian brain is so inscribed that the two 

 Psalteria coincide (see page 173). 



The similarity of the two brains is at once apparent; one notes that the 

 Gyrus limb — cornu Ammonis — of the one corresponds to the same feature 

 of the other; indeed, one recognizes that the olfactory tract, which enters 

 into Ammon's horn anteriorly from the base, exactly corresponds in the two 

 figures. Compare especially Fig. 114, where, in the brain of the lizard, this 

 bundle appears just like the above. But this experiment has not its sole 

 significance on the morphological side. It should also show especially in 

 what directions the farthest development of the brain proceeded, using the 

 reptile's as a starting-point. In the first place, one recognizes that from the 

 brain of the reptile to that of the marsupial is a much shorter step than that 

 from the brain of the marsupial to the brain of man. 



But only in mammals does the mantle with the cortical portions become 



