520 OF THE NERVOUS SYSTEM AND ITS ACTIONS. 



Such are the soft commissure, which also extends between the Thalami ; 

 the Pons Tarini, which extends between the two crura or peduncles of 

 the Cerebrum ; and the Tuber Cinereum, which seems to unite the 

 optic tracts with the thalami, the corpus callosum, the fornix, &c., and 

 to be a common point of meeting for several distinct groups of fibres. 



916. The anterior and posterior parts of the hemispheres, moreover, 

 are connected by longitudinal Commissures, of which some lie above, 

 and some below, the corpus callosum ; and of these, also, a part belong 

 to the Sensory Ganglia. Above the transverse fibres of the corpus 

 callosum, there is a longitudinal tract on each side of the median line, 

 which serves to connect the convolutions of the anterior and posterior 

 lobes of the brain. And above this, again, is the superior longitudinal 

 commissure, which is formed by the fibrous matter of the great convolu- 

 tion nearest the median plane on the upper surface of the brain, and 

 which connects the convolutions of the anterior and middle lobe with 

 those of the posterior. Beneath the great transverse commissure, we 

 find the most extensive of all the longitudinal commissures, namely, the 

 Fornix. This is connected in front with the optic thalami, the mammil- 

 lary bodies, the tuber cinereum, &c. ; and behind, it spreads its fibres 

 over the hippocampi (major and minor), which are nothing else than 

 peculiar convolutions that project into the posterior and descending 

 cornua of the lateral ventricles. The fourth longitudinal commissure is 

 the tcenia semicircular is, which forms part of the same system of fibres 

 with the fornix ; connecting the corpus mammilare and thalamus opticus 

 with the middle lobe of the cerebral hemisphere. If, as Dr. Todd has 

 remarked, we could take away the corpus callosum, the gray matter of 

 the internal convolution, and the ventricular prominence of the optic 

 thalami, then all these commissures would fall together, and become 

 united as one and the same series of longitudinal fibres. It is curious 

 that there should be no direct communication between the Cerebral 

 hemispheres and the Cerebellum ; the only commissural band between 

 them being the processus a cerebello ad testes, which passes onwards, 

 through the Tubercula Quadrigemina, to the Thalamus Opticus on each 

 side. This would seem to confirm the idea of the complete distinctness 

 of their functions. 



917. The Cerebrum appears to be the instrument of all those psychi- 

 cal operations, which are superadded, in Man and the higher Verte- 

 brata, to mere sensations. The impressions which are merely felt in 

 the sensorium, give rise, when they pass upwards into the Cerebrum, 

 to Ideas, which then become the material (so to speak) of all the higher 

 mental processes. These processes may be ranked under two dis- 

 tinct heads, namely, the Emotional and the Intelligential ; the former 

 being most intimately connected with the sensations which prompt them, 

 whilst the latter are commonly of a much more abstract character. 

 The Emotions may, in fact, be considered as feelings of pleasure or pain 

 associated with particular classes of ideas ; and it is this association 

 which gives them the character of the moving or active powers of the 

 mind, and which makes them, either directly or indirectly, the springs 

 of the greater part of our actions. When strongly excited, the Emo- 

 tions may produce movements which the Will may not be able to re- 



