534 THE POPULAR SCIENCE MONTHLY 



Edinger 2 has shown that to the primitive division of the brain of 

 the vertebrate (or the paleencephalon), which is the bearer of the 

 reflexes and the instincts, there has been gradually added with peculiar 

 adjustments a newer division (the neencephalon), which corresponds to 

 the cerebrum, in which alone is centered the power of association, and 

 of forming memory images. In proportion as the cerebral cortex 

 increases, the primitive brain recedes, while in a corresponding ratio 

 intelligence rises, and purblind instinct wanes. 



A very interesting fact for us, as Edinger has further shown, is 

 that while the cerebral cortex of the bird is more highly developed 

 than in reptiles, the far greater bulk of the brain is mainly due to an 

 enlargement of the primitive division, the parts of which reach a size 

 and proportion nowhere else seen, while at the same time they are very 

 generally connected with the cerebrum. From these facts alone we are 

 warranted to infer that while birds are intelligent and able to form 

 associations of some sort freely, they must be animals in which the 

 instincts are developed to an extraordinary degree of perfection, com- 

 parable in large measure with those of the social insects. All this is 

 amply proved by their behavior, and in describing the activities of birds 

 it seems best to discriminate as sharply as possible their instinctive 

 activities from the operations of intelligence, assuming, until the con- 

 trary is proved, that their reflexes and instincts pertain exclusively to 

 the primitive division of the brain, as already stated, while the power 

 of association is lodged in the cerebrum alone. 



Not only does the bird's brain possess great basal ganglia of which 

 the huge optic lobes are most prominent, but a large cerebellum, and 

 very diminutive, possibly rudimentary olfactory lobes. These facts 

 find their clear counterpart in behavior. Large optic nerves, optic 

 tracts and lobes, are to be expected in animals like the birds, which 

 possess the keenest eyes of any vertebrates known, and which depend so 

 largely upon vision for finding their food and for detecting their 

 enemies and their friends. 



The wonderful powers of flight, possessed by birds as a class, may 

 not only be long sustained, as in the golden plover which is supposed 

 to make the journey from Nova Scotia to the West Indies, a distance 

 of 1,700 miles, in a single flight, but is often so rapid that fatal results 

 would follow were the control of direction less precise. Their move- 

 ments clearly demand an organ for the most perfect coordination of 

 their skeletal muscles, and such is undoubtedly found in their large 

 cerebellum, the action of which is purely reflex. Thus swallows are 

 often seen to enter a barn, where they have their nests, at a perilously 

 rapid rate, through cracks or holes, barely large enough to admit their 



2 Edinger, Ludwig, " The Relations of Comparative Anatomy to Compara- 

 tive Psychology" (translated by H. W. Rand), Journ. of Comp. Neurology and 

 Psychology, Vol. XVIII., No. 5, 1908. 



