evoke similar Movements. But would such facts entitle us to infer that these Sensory Ganglia contain 'motor' Centres? Assuredly not: no more than we should be entitled to call the sensory cells' on the ingoing side of a simple mechanism for some Reflex Action motor cells,' simply because a stimulus issues from them which ultimately evokes the Movement-that is, after it has passed through other nerve elements which, by common consent, are regarded as 'motor cells.'

The nervons fibres that extend from the Cerebral Cortex, in higher animals and in Man, down to the Corpora Striata are, in their nature, strictly comparable with the fibres connecting the 'sensory' and the 'motor' Cells in an ordinary nervous mechanism for Reflex Action. Such currents from 'sensory' cells may pass in the same horizontal plane, they may have to ascend, or, as frequently happens, they may descend to 'motor' cells situated at a lower level.*

The Corpora Striata, conjointly with the Cerebellum, are doubtless specially called into activity by the Cerebral Cortex, in ways which are most important though they cannot be precisely defined. These organs, as we

* On account of the variability of this relation, therefore, such nerve fibres cannot be considered to be invariably in relation either with ingoing' or with 'outgoing' currents. We may distinguish them by the name of ‘internuncial fibres,' with the understanding that in different parts of the Nervous System currents are transmitted along them in an ascending, a horizontal, or in a descending direction. Still, as the stimuli emanating from the Sensory Centres and their annexes in the Cerebral Cortex, at once take a downward direction to the Corpora Striata, it will be most ccnvenient in this case, to speak of the origin of outgoing' currents as being from the Cerebral Cortex itself, and to regard certain of its Centres as occupying what has been aptly termed the bend of the stream that is the regions where 'ingoing' currents end or give place to outgoing' currents.

contend, are the great motor ganglia through which cortical stimuli resulting from so-called 'Volitional' or Intellectual guidance operate. If, indeed, what has been set forth in this chapter gives anything like a true account of the relations existing between Voluntary and Automatic Movements, not another word need here be said against the general point of view upon which Hughlings Jackson and Ferrier rest their hypothesis as to the existence of 'motor centres' in the Cerebral Cortex, nor against the view that the mechanisms for Voluntary Movements are 'organized' in regions altogether apart from those concerned with the execution of Automatic Movements.

What has been said in the earlier parts of this chapter in reference to the origin and nature of "Volitional' stimuli, together with what has been stated above, make it possible to explain the results of irritation and destruction of certain fronto-parietal areas of Grey Matter and of the white matter intervening between them and the Corpora Striata, without in the least countenancing the supposition that motor centres' exist in the Cerebral Convolutions.*

The Centres in question are rather sensory' in nature, and are probably intimately concerned with certain groups of Kinæsthetic Impressions-whatever other functions they may subserve, or with whatever other centres they may be in intimate relation. We have, indeed, seen

* We have here, in fact, to do with a misconception very similar in kind to that which previously led Foville and others to regard the Cerebellum as a Sensory Organ (p. 504) simply because 'internuncial fibres' enter it from various sensory nuclei or ganglia. To argue that groups of cells have motor functions, merely because stimuli issuing from them evoke movements when they impinge upon motor ganglia, is quite on a par with the argument that an organ has sensory functions because fibres come to it from sensory

cells.

reason for believing that the Kinæsthetic must be in the closest functional relationship both with the Visual and with the Auditory Centres. From one or more (but perhaps more especially from the first) of these inter-related Perceptive Centres or their annexes, internuncial fibres' issue, by which they are brought into functional relations. with the great underlying motor ganglia-the Corpora Striata.

Stimulation of certain sets of such internuncial fibres' should produce special Choreic or Convulsive Movements; destruction of them should produce Paralysis; and, looking to the direction in which they transmit their stimuli, analogy would lead us to infer that the severance of their connections with cortical nerve-cells might lead to small bands or tracts of 'descending degenerations' between the seats of such severance and the corresponding Corpus Striatum-yet these are the results the occurrence of which is so confidently relied on by some in support of the motor' functions of such portions of the Cerebral Cortex.

AFTER the first

CHAPTER XXVII.

CEREBRAL MENTAL SUBSTRATA.

Sensation' nothing strictly answering to this term exists. We only consciously realize any impression, as of such and such a nature, by automatic comparison of it with other impressions which have gone before it. A simple Sensation' can, in fact, scarcely exist in consciousness, nor can it be imagined by us in our present phase of mental evolution. Our so-called 'Sensations' are really Perceptions. In one and the same act or state each of them embodies Feeling and Intelligence in indissoluble connection.

A seat of simple' or 'brute' Sensation is, therefore, not to be looked for. The seats of conscious sensibility in the only intelligible phase in which such states can exist for us are centres for Perception*.

As the act of Perception involves the automatic comparison of present impressions with revived past impressions of the same kind, as well as of some or all other kinds of impressions capable of being yielded by the Object perceived, it happens that even in the simplest socalled Sensation' the conjoint activity is necessitated of no one limited tract of convolutional grey matter-but rather of widely extended cell-and-fibre mechanisms corresponding, it may be, with many more or less diffused and complexly related Perceptive Centres (p. 522).

Seeing that each Perceptive Centre forms the basis or starting point of different processes of Ideation, and,

* See pp. 176, 524, and “Nature," Jan. 20, 1870, p. 309.

therefore, of Thought, and that the several centres must have the same kind of relation to Emotion, we may find therein additional reason for the belief that the different Perceptive Centres are diffuse in seat, and that widely separated parts of the Cerebral Hemispheres are probably knitted together for simultaneous action even in the simplest sensory Perception-containing, as this process does, the germs of Thought and Emotion, to say nothing of Volition'. 6 * And although these diffuse, but functionally unified, nervous networks may differ much from ordinary Centres' (owing to their assumed lack of topographical distinctness and exclusiveness), it is still convenient to be able to refer to such networks as

Centres.' But in addition to the complex perceptive mechanisms in relation with the five senses,' there are also other Cerebral Centres for ingoing impressions, some of which are, when in action, habitually attended by more or less of Consciousness, whilst others are as constantly devoid of any such accompaniment. Yet all these 'Centres '—quite irrespective of the degree of vividness of the subjective accompaniments dependent upon their activity-are probably situated in some portions of the Cerebral Cortex. +

* See Dr. Lombard, “On the effect of Intellectual and Emotional Activity on the Temperature of the Head," in "Proceed. of Royal Society," 1878, p. 462.

† Among these a 'sense of Space' Centre ought, perhaps, to be included, the activity of which would, however, be of less importance for Man than for many of the lower animals (pp. 214-219). The instinctive and untaught migrations of young Birds may depend much upon the automatic activity of this Centre, and are phenomena of the same order as the instinctive fear of the young Turkey on hearing the cry of the Hawk (p. 189), or the instinctive appreciation of food and distance which enables the young Chick to snap at and capture a Bee (p. 188). In all these cases we have to do with automatic Perceptions, as well as with Automatic Movements.