686 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



that there is a large class of motions in which the Brain has no concern, and 

 that the removal of the Cerebral hemispheres is not incompatible (even 

 among the higher Vertebrata) with the prolonged maintenance of a sort of 

 inert and scarcely conscious life. Still, it has been usually maintained, and 

 with great show of reason, that the Cerebrum is the instrument of all psychical 

 operations, and the originator of all the movements which could not be as- 

 signed to the reflex action of the Spinal Cord. An attempt has been made, 

 however, in the preceding pages, to show that this view is not correct; and 

 that there is a class of actions, neither excito-motor nor voluntary, hut di- 

 rectly consequent upon Sensations, and constituting (with the excito-motor) 

 the truly instinctive actions, which may be justly assigned to certain ganglionic 

 centres not less independent of the Cerebrum than is the Spinal Cord itself. 

 It has been further pointed out that the Cerebrum must be considered in the 

 light of an organ sup&radded for a particular purpose or set of purposes, and 

 not as one which is essential to life ; that it has no representative among the 

 Invertebrata (except in a few of the highest forms, which evidently present 

 a transition towards the Vertebrated series) ; and that, at its first introduc- 

 tion in the class of Fishes, it evidently performs a subordinate part in the 

 general actions of the Nervous System. Hence, whatever be the function, 

 or set of functions, we assign to the Cerebrum, we must keep in view the 

 special character of the organ ; and we must never lose sight of the fact, that 

 its predominance in Man does not deprive other parts of their independent 

 powers, although it may keep the exercise of those powers in check, and may 

 considerably modify their manifestations. 



558. Before proceeding to inquire into the Physiology of the Cerebrum, 

 we may advantageously take notice of some of the leading features of its 

 structure. 1 



In the first place, it forms an exception to the general plan on which the elements 

 of ganglionic centres are arranged ; in having its vesicular substance on the exterior, 

 instead of in the central part of the mass. The purpose of this is probably to allow 

 the vesicular matter to be disposed in such a manner as to present a very large surface, 

 instead of being aggregated together in a more compact mass; and by this means to 

 admit, on the one side, a more ready access of the bloodvessels which are so essential 

 to the functional operations of this tissue, as well as a more ready communication, on 

 the other, with the vast number of fibres by which its influence is to be propagated. 

 There is no reason whatever to believe, that the relative functions of the vesicular and 

 fibrous substances are in the least altered by this change in their relative position ; 

 indeed, the results of observation upon the phenomena of disordered Cerebral action 

 are such as to afford decided confirmation to the doctrine now generally accepted, that 

 the action of the Vesicular matter constitutes the source of nervous power, whilst the 

 Fibrous structure has for its office to conduct the influence thus generated to the points 

 at which it is to operate. The purpose of this arrangement is further evidenced by 

 the fact, that, in all the higher forms of Cerebral structure, we find a provi-ion for a 

 still greater extension of the surface at which the vesicular matter and the hlood- 

 ves.-els may come into relation ; this being etl'eeted by the plication of the layer of 

 vesicular matter into "convolutions," into the sulci between which the highly vas- 

 cular membrane known as the " pia mater " dips down, sending multitudes of small 

 vessels from its inner surface into the cortical substance. The convolutions of the 

 Brain 2 are extremely complicated in their arrangement, but they can be divided into 

 groups by certain easily recognized fissures, and are individually identified and named. 

 Tile more important of them only need be described here. The outer and under 

 surface of each hemisphere is divided into five lobes as follows. Tracing the deep 



.! For further details of the minute anatomy of the Cerebral substance, see Lock- 

 hart Clarke in the Proceedings of the Royal Society, vol. xii, No. 57. 



2 For accurate descriptions of which see Prof. Turner's Pamphlet, 1866; Gratiolet, 

 Sur les Plis Cerebrau x de I'Hommn, etc., 1854; L. Marshall on the Brain of a Bush- 

 woman, etc., Proc. Roy. Soc , 1863, Quain and Sharjiey's Anatomy, vol. ii, p. 531, 

 and Ecker's pamphlet on the Convolutions of the Brain. 



