SUMMAEY. 



THE brain is more or less spherical or tabulated in all animals ; in man, at 

 the upper part of its hemispheres, there is an extensive fissure, and one more or 

 less deep in many of mammalia ; but in some of these and the other classes there is a 

 very little, if any, separation. Convolutions answer a particular and not a general 

 purpose ; they are very deep in man, and some of mammalia ; but in others and the 

 several . inferior classes they hardly exist. The great commissure is very extensive in 

 man and such of mammalia as have the hemispheres high and large ; it faintly exists 

 in others, in which the lobes only just inclose the lateral ventricles ; it is not present 

 in the three lower classes. Ventricles vary in all the classes ; the lateral has a 

 posterior horn in simise proportioned to the posterior lobe, so that in some it is a 



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mere chink ; in birds it extends more posteriorly, at which part its parietes are very 

 thin ; it is placed anteriorly in amphibia and fishes. The third ventricle lies between 

 the thalami in mammalia and birds; in birds it extends into the optic lobes; in 

 amphibia and fishes it is continued from the same surface with the lateral. The 

 fourth ventricle exists in all ; and in birds, amphibia, and fishes, extends into the optic 

 lobes and cerebellum. The transparent septum exists in mammalia only; in 

 birds, the striated septum supplies the place of it and the great commissure. The 

 fornix exists in mammalia only ; in birds, the floor of the lateral ventricle supplies 

 its place. The great hippocampus exists in mammalia, there is a smaller eminence 

 resembling it in birds, but not in the other classes. The striated body exists in the 

 three superior classes ; in mammalia it is similar to that in man, but very different 



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