THE CBEEBEUM OE PEOSEKCEPHALON. 



175 



primary optical centers to the occipital lobes, and I will show later how in 

 mammals all of those functions which we conceive as "seeing with under- 

 standing, recognition and interpretation" are dependent npon the entirety 

 of the occipital lobe. Thus, in hirds, first in the series, the primary optical 

 apparatus is connected with the cortical mechanism. Undoubtedly a greater 

 capacity for service is thus made possible for the visual apparatus. 



It will now be more easily understood how birds work — in part — ^with 

 very highly developed possibilities for visual memories. The interpretation 

 of olfactory impressions may be sufficient for the supply of life-necessities for 

 the earth-groveling lower vertebrates, but for birds the same thing would 

 not be advantageous. For, flying far above their food, their homes, etc., they 



Pig. 121. — Composite' of several lateral sagittal sections from a, pigeon's brain 

 showing the course of the Tr. oecipito-meseneephalicus. 



must be able to recognize these by sight, and, more than that, to differentiate 

 them from all other similarly appearing objects. Eecall in this connection 

 the unerring swoop of the bird of prey upon its victim; the migrations, the 

 certain return of the carrier-pigeon, etc. 



Another bundle which arises in the cortex of the avian brain has been 

 mentioned already — the Tr. Septo-mesencephalicus (Fig. 115). This stands 

 in close connection with the terminations of the optic nerve and with the 

 sensory functions of the midbrain. Eegarding the functions whose bearer it 

 is we know nothing as yet with much certainty. Its severing does not cause 

 disturbance of vision (Jensen), nor does it cause indubitable motor dis- 

 turbances. 



