Page:Encyclopædia Britannica, Ninth Edition, v. 19.djvu/50

Rh 40 PHYSIOLOGY [NERVOUS Longi tudinal be distributed to tlic central convolutions of the cerebrum, (i) Fibres issuing from the corpus callosuin and descending into the internal capsule, (k) Fibres of the external capsule which ascend from the crusta aud ultimately reach the cortex through the corona radiata. In addition to the peduncular fibres above enumerated, all of which belong to what may be termed the system of the internal capsule and corona radiata, fibres from the fornix, ta-nia semi- circularis, outer layer of septum hioidum, and the fillet of the cms also pass from below upwards to the cortex of the hemispheres (Ross). (2. ) Longitudinal or Collateral fibres. (a) Fibres running im mediately below the surface of the cortex^ and connecting the grey fibres of matter of adjacent convolutions, (b) Fibres in the gyrus fornicatus, cere- a convolution immediately above the corpus callosuin. It is said brum. that bands of these fibres arise in the anterior perforated space and pass completely round the corpus callosuin to end in the same per forated space, and that offsets of these fibres pass upwards and backwards to reach the summits of the secondary convolutions derived from the gyrus fornicatus near the longitudinal fissure. (c) Longitudinal fibres of the corpus callosum (nerves of Lancisi), connecting the anterior and posterior ends of the callosal convolu tion, (d) Longitudinal septal fibres, lying on the inner surface of the septum lucidum, and entering into the gyrus fornicatus. (c) The fasciculus uncinatus, passing across the bottom of the Sylvian fissure and connecting the convolutions of the frontal and temporo- sphenoidal lobes. (/) The longitudinal inferior fasciculus, connect ing the convolutions of the occipital with those of the temporal lobe. Com- (3.) Transverse or Commissural Fibres. cere brum. missural (a) Many, if not all, of the fibres of the fibres of corpus callosum pass transversely from 1 one side to the other and connect corre-i spending convolutions in the hemispheres. This is the generally accepted view ; but 1 Professor Hamilton of Aberdeen has recently r ^ stated that his preparations show that there 9 A^ is no such commissural system between con- &quot;|S f volutions, and that the fibres decussating in the corpus callosum are not continued to convolutions on the other side, but pass downwards, (b) The fibres of the anterior commissure wind backwards through the lenticular nuclei to reach the convolutions round the Sylvian fissure, (c) The fibres of the posterior commissure run through the optic thalami. 1 Arrange- Arrangement and Structure of Grey Mat- raent tcr. The grey matter in the medulla and and basal ganglia has been already considered, structure A web or sheet of it is also thrown over the of grey surface of the cerebrum, and forms the outer matter, portion of all the convolutions. The cor tical substance consists of cells and fibres imbedded in a matrix similar to the netiroglia of the spinal cord. It may be divided into five layers, which merge into each other by almost insensible gradations. The most ex ternal layer consists of delicate nerve-fibres, neuroglia, and a few small round cells desti tute of processes (see fig. 28). Going deeper we find cells of a characteristic pyramidal form, the largest being in the deepest layer. Their bases are turned inwards, and their apices towards the surface of the convolu tion. Cleland states that fibres passing from the apices are continuous with the delicate fibres found on the very surface of the cor tex. In the ascending frontal convolu tions Betz and Mierzejewski have found pyramidal cells two or three times larger than those of other regions of the cortex, and these have been termed &quot; giant-cells. &quot; Bl / S& All the pyramidal cells, no doubt, anasto- p,. 23. (After Meym-rt.) mose by their processes, and give origin to Vertical section of a fur- the nerve-fibres of the white substance, but row of third cerebral con- it i, rarely possible to trace the fibres from ^SttoSSin S cell to cell. A consideration of these ana tomical facts, along with those mentioned in cal corpuscles ; 2, layer of close-set small pyra midal corpuscles ; 3, connexion with the comparative anatomy of, a , , - the brain, shows that the cerebral hemi- Start c^usckT! I, spheres are in intimate connexion by fibres layer of small close-set with all the other portions of the cerebro- &quot;Tegular-shaped corpus- spinal system. Further, they are not only ^^SEfS intricate in structure themselves, but the the claustrum); m, mc- commissurAl sets of fibres indicate that dullary lamina, there is harmony of function between one part and another. In 1 In preparing the foregoing sketch of the fibres of the cerebrum the writer is much indebted to Ross, Diseases of the Nervous Sj stem. determining the function of so complicated an apparatus recourse must be had to the evidence (1) of development, (2) of compara tive anatomy, (3) of human anatomy, (4) of the observed effects of disease before and after death, and (5) of experiment. Facts have already been collected from the first three of these fields of inquiry, all tending to show that the grey matter of the hemi sphere is associated with the manifestation&quot; of intelligence in its various forms. The phenomena of disease support the same con clusion. Diseases producing slow changes in the layer of grey matter on the cortex are invariably associated with mental disturb ance, such as melancholia, mania, or dementia. If the grey matter be suddenly injured or submitted to compression, as by a blow causing fracture and depression of a portion of the skull, or the effusion of fluid consequent on inflammation, unconsciousness is a certain result. _ So long as the pressure continues there is no con sciousness ; if it be removed, consciousness may soon return. On the other hand, if the disease affect the white matter of the central portions or the ganglia at the base, there may be paralysis or con vulsions without consciousness being affected. All the facts, therefore, of pathology relating to the brain indicate that the grey matter on the surface of the hemispheres is the organ of conscious ness and of all mental operations. This statement is now an axiom of medical science, and the basis of the rational treatment of the insane and of all maladies of the central nervous organs. Two methods of experiment upon the cerebrum have usually been followed, and both have yielded important results. (a.) Removal. Flourens and the older observers were aware of Remcr- the fact that as successive slices of grey matter are removed from of gre- the surface of the cere- ^s*m^=^-&amp;gt;?^ matte! brum an animal be comes more dull and stupid, until at last all indications of percep tion and volition dis appear. A pigeon in this condition (see fig. 29), if carefully fed, may live for many months ; to quote from Dalton - &quot; The effect of this muti- Fio. 29. Pigeon, in which the cerebrum has been lalion is simply to plunge injured or removed, the animal into a state of profound stupor, in which it is almost entirely inattentive to surrounding objects. The bird remains sitting motionless upon his perch or standing upon the ground, with the eyes closed and the head sunk between the shoulders. The plumage is smooth and glossy, but is uniformly expanded by a kind of erection of the feathers, so that the body appears somewhat puffed out, and larger than natural. Occasionally the bird opens its eyes with a vacant stare, stretches its neck, perhaps shakes its bill once or twice, or smooths down the feathers upon its shoulders, and then relapses into its former apathetic con dition.&quot; Similar observations have also been made on reptiles and mammals, but the latter survive the operation for a comparatively short time. In watching such an animal it is difficult to divest one s mind of the belief that it still feels and sees and hears. It may be observed that it rarely makes movements unless stimulated from without. Thus it may remain motionless for many hours ; but if pushed, or gently touched, it moves. As remarked by Prof. M. Foster &quot; No image, either pleasant or terrible, whether of food or of an enemy, pro duces any effect on it, other than that of an object reflecting more or less light. And, though the plaintive character of the cry which it gives forth when pinched suggests to the observer the existence of passion, it is probable that is a wrong interpretation of a vocal action ; the cry appears plaintive, simply lie- cause, in consequence of the completeness of the reflex nervous machinery and the absence of the usual restraints, it is prolonged. The animal is able to execute all its ordinary bodily movements, but in its performance nothing is ever seen to indicate the retention of an educated intelligence.&quot; (b. ) Electrical Stimulation of Surface of Brain. It is remarkable Electi that, although many of the early workers in cerebral physiology stimu stimulated the surface of the brain by electric currents, they tion c observed no effect, and therefore Magendie, Matteucci, Longet, brain- Weber, Budge, Schiff, and others taught that irritation of the surfac surface of the hemispheres called forth no muscular movements ; and it was generally accepted that the grey matter on the cortex of the brain was entirely concerned in the phenomena of sensation, volition, and intellectual action. During the Franco -Germ an war in 1870 Hitzig had occasion to apply galvanism to a portion of the exposed brain of a wounded soldier, and he observed contrac tions of the muscles of the eyeball. When peace was restored, experiments were made on the lower animals by Hitzig ami Fritsch, in which a portion of exposed brain was irritated by a continuous current, and it was observed that the phenomena took place on opening and closing the current. By these experiments the German observers discovered that, when certain areas of grey matter were stimulated, contractions of certain muscles occurred, and they were thus able to map out areas for groups of muscles. Immediately afterwards the research was taken up by Professor David Ferrier of King s College, London, who, using a Faradaic instead of a continuous current, greatly extended the field of inquiry, and obtained many important results, which are not only