286 SPECIAL PHYSIOLOGY. 



common sensation, as the olfactory, optic, auditory, and gustatory 

 ganglia have to their respective nerves. Disease of the optic thala- 

 mus, is followed by hemiplegia, i. e., paralysis of both sensation and 

 voluntary motion of one-half of the body, on the opposite side: disease 

 of the corpus stria-turn has, however, the same effect. It has also been 

 suggested that the optic thalami may be the organic seats of the emo- 

 tional part of our mental nature, in which case, they must act as sen- 

 sorial centres, recognizing the changes which occur in the production 

 of ideas, within the cerebral hemispheres. A still further extension 

 of this view, regards the thalami as the seats of consciousness of the 

 mental state, ideational, emotional, rational, and volitional ; in this 

 case, just as the sensory nerves and sensory tracts bring impressions 

 from without, to the common sensorium in the optic thalami, and pro- 

 duce sensational consciousness, so it is supposed that the convergent 

 or descending fibres, which pass from the cerebral hemispheres to the 

 thalami, and which Reil named, as we shall see, the nerves of the inter- 

 nal senses, may be the paths by which the various actions of the brain 

 itself, may be recognized by the same sensorium, and so cause all the 

 varieties of mental consciousness. (Carpenter.) This ingenious view 

 is, at least, highly suggestive. 



From the present state of our knowledge, we may suppose, first, 

 that the gray matter of these large ganglionic masses, the optic thala- 

 mi, together with the gray matter diffused through the peduncles, pons, 

 medulla oblongata, and spinal cord, constitute the true immediate 

 centres for the reception of all kinds of sensory impressions, with the 

 exception of those of smell, viz., those of common sensation, the sense 

 of temperature, the tactile sense, perhaps the muscular sense, and the 

 sensations of sight, hearing, and taste. Secondly, it would appear 

 that in other parts of the gray matter, this portion of the great cere- 

 bro-spinal axis, from the corpora quadrigemina, corpora striata, and 

 thalami, downwards through the peduncles, pons, medulla oblongata, 

 and spinal cord, we have & great centre of motorial excitability (Shar- 

 pey), through the agency of which, all the involuntary reflex move- 

 ments, whether sensori-motor or excito-motor, are performed. 



Whether the large mass of gray matter, above supposed to be en- 

 gaged in sensation, is itself the true sensorium, or actual seat of the 

 conscious sensation of -bodily conditions, as is commonly believed, or of 

 both bodily and mental states, as suggested by Reil and Carpenter, 

 or whether the impressions produced in it, according to the sense which 

 excites them, must react, in some way, along the radiating fibres which 

 expand from their upper end into the cerebral hemispheres, in order 

 that conscious sensation should be realized, is unknown. It would 

 seem certain, however, that perception or the association of sensations 

 with their causes, ideation or the formation of ideas, memory, and the 

 processes of comparison, combination, and determination of differences, 

 which are implied in reasoning, and, lastly, the resulting volition or 

 will, involve the material operation of the cerebral hemispheres. 



Furthermore, whether, in the exercise of this will, in producing 

 voluntary movements, the conducting fibres are prolonged directly 

 downwards from the cerebral hemispheres through the cerebral ped- 



