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For there is a very marked groove in every such skull, as in the human skull which indicates the line of attachment of what is termed the 'tentorium' a sort of parchment-like shelf, or partition, which, in the recent state, is interposed between the cerebrum and cerebellum, and prevents the former from pressing upon the latter.
Negative results, as regards specific faculties, were obtained from all localized irritations of the cerebrum, and Flourens was forced to conclude that the cerebral lobe, while being undoubtedly the seat of higher intellection, performs its functions with its entire structure.
The surface of the brain is very uneven. There are a great many folds separated by grooves. Some of these are more than an inch deep. =Parts of the Brain.= The brain is divided into three chief parts. The upper and larger part is called the big brain or cerebrum. The lower part behind is the little brain or cerebellum.
In particular the corpus callosum, that unites the two cerebral hemispheres, is only developed in the Placentals. Other structures for instance, in the lateral ventricles that seem at first to be peculiar to man, are also found in the higher apes, and these alone. It was long thought that man had certain distinctive organs in his cerebrum which were not found in any other animal.
The SECOND is that of RESPIRATION: like volition, the motive influence in respiration passes in a DIRECT LINE from one point of the nervous system to certain muscles; but as voluntary motion seems to originate in the cerebrum, so the respiratory motions originate in the medulla oblongata: like the voluntary motions, the motions of respirations are spontaneous; they continue, at least, after the eighth pair of nerves have been divided.
The cerebellum increases with the greater locomotive powers of the animal. But its development is evidently limited. The large brain, or cerebrum, is in fish hardly as heavy as the mid-brain; in amphibia the reverse is true. In higher recent reptiles the cerebrum would somewhat outweigh all the other portions of the brain put together.
If this be so, it would seem probable, a priori, that other intellectual acts are also distinct from consciousness. For present purposes the activities of the cerebrum may be divided into the emotional and the more strictly-speaking intellectual acts. A little thought will, I think, convince any of my readers that emotions are as purely automatic as the movements of the frog's hind leg.
Its charts are almost as misleading concerning character as photographs. And photography may be described as the art which enables commonplace mediocrity to look like genius. The heavy-jowled man with shallow cerebrum has only to incline his head so that the lying instrument can select a favorable focus, to appear in the picture with the brow of a sage and the chin of a poet.
The convolutions of the cerebrum are without doubt associated with all those higher actions which distinguish man's life; but all the convolutions are not of equal importance. Thus it is probable that only the frontal part of the brain is the intellectual region, while certain convolutions are devoted to the service of the senses.
The impressions received by the cerebrum and cerebellum are waves of molecular disturbance sent up along centripetal nerves from the lower centres, and presently drafted off along centrifugal nerves back to the lower centres, thus causing the myriad movements which make up our active life.
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