684 



REMOVAL OF THE CEREBRUM. 



a peculiar cry is emitted in some cases of pressure or inflammation rendering the 

 cerebral hemispheres inactive. 



Observations on somnambulists show that in man, also, complete harmony 

 of all movements may be retained, without the assistance of the will or conscious 

 impressions aud perceptions. As a matter of fact, many of our ordinary movements 

 are accomplished without our being conscious of them. They take place under the 

 guidance of the basal ganglia. 



The degree of intelligence in the animal kingdom is in relation to the size of the cerebral 

 hemispheres, in proportion to the mass of the other parts of the central nervous system. Taking 

 the brain alone into consideration, we observe that those animals have the highest intelligence 

 in which the cerebral hemispheres greatly exceed the mid-brain in weight. The mid-brain is 

 represented by the optic lobes in the lower vertebrates, and by the corpora quadrigemina 

 in thf higher vertebrates. In tig. 483, VI, represents the brain of a carp ; V, of a frog ; 

 and IV, of a pigeon. In all these cases 1 indicates the cerebral hemispheres; 2, the optic 

 lobes ; 3, the cerebellum ; and 4, the medulla oblongata. In the carp, the cerebral hemi- 

 spheres are smaller than the optic lobes ; in the frog, they exceed the latter in size. In 

 the pigeon, the cerebrum begins to project backward over the cerebellum. The degree of 

 intelligence increases in these animals in this proportion. In the dog's brain (fig. 483, II) 

 the hemispheres completely cover the corpora quadrigemina, but the cerebellum still lies 

 behind the cerebrum. In man the occipital lobes of the cerebrum completely overlap the 

 cerebellum (fig. 479). [The projection of the occipital lobes over the cerebellum is due to the 

 development of the frontal lobes pushing backwards the convolutions that lie behind them, 

 and not entirely to increased development of the occipital lobes.] 



Meynert's Theory. According to Meynert, we may represent this relation in another way. 

 As is known, fibres proceed downwards from the cerebral hemispheres, through the crusta or 

 basis of the cerebral peduncle. These fibres are separated from the upper fibres or tegmentum 

 of the peduncle by the locus niger, the tegmentum being connected witn the corpora quadrige- 

 mina and the optic thalamus. The larger, therefore, the cerebral hemispheres, the more 

 numerous will be the fibres proceeding from it. In fig. 461, II, is a transverse section of the 

 posterior corpora quadrigemina, with the aqueduct of Sylvius and both cerebral peduncles of an 

 adult man ; ;;, p, is the crusta of each peduncle, and above it lies the locus niger, s. Fig. 461, 

 IV, shows the same parts in a monkey ; III, in a dog ; and V, in a guinea-pig. The crusta 

 diminishes in the above series. There is a corresponding diminution of the cerebral hemi- 

 spheres, and, at the same time, in the intelligence of the corresponding animals. 



Sulci and Gyri. The degree of intelligence also depends upon the number and depth of the 

 convolutions. In the lowest vertebrates (fish, frog, bird) the furrows or sulci are absent (fig. 

 461, IV, V, VI) ; in the rabbit there are two shallow furrows on each side (III). The dog has 

 a completely furrowed cerebrum (I, II). Most remarkable is the complexity of the sulci and 

 convolutions of the cerebrum of the elephant, one of the most intelligent of animals. Never- 

 theless, some very stupid animals, as the ox, have very complex convolutions. 



The absolute weight of the brain cannot be taken as a guide to the intelligence. The 

 elephant has absolutely the heaviest brain, but man has relatively the heaviest brain. [We 

 ought also to take into account the complexity of the convolutions and the depth of the grey 

 matter, its vascularity, and the extent of anastomoses between its nerve-cells.] 



Time an Element in all Psychical Processes. Every psychical process requires 

 a certain time for its occurrence a certain time always elapses between the 

 application of the stimulus and the conscious reaction. 



