610 NERVOUS SYSTEM. 



can be judged from what is positively known of the action of the encephalic 

 centres, the pain under these conditions is perceived by some nerve-centre, 

 probably in the pons Varolii, but the impression is not conveyed to the 

 cerebrum and is not recorded by the memory. 



Taking all the experimental facts into consideration, the following seems 

 to be the most reasonable view with regard to the action of the pons Varolii 

 as a nerve-centre : 



It is an organ capable of originating impulses giving rise to voluntary 

 movements, when the cerebrum, corpora striata and the optic thalami have 

 been removed, and it probably regulates the automatic voluntary movements 

 of station and progression. Many voluntary movements, the result of intel- 

 lectual effort, are made in obedience to a stimulus transmitted from the cere- 

 brum, through conducting fibres in the pons Varolii, to the motor conduc- 

 tors of the cord and the general motor nerves. 



The gray matter of the ports Varolii is also capable of perceiving painful 

 impressions, which, when all of the encephalic ganglia are preserved, are 

 conducted to and are perceived by the cerebrum, and are remembered ; but 

 there are distinct evidences of the perception of pain, even when the cere- 

 brum has been removed. 



Directions of the Fibres in the Cerebrum. Fibres pass from the cerebral 

 hemispheres to the cerebellum. Commissural fibres connect the cerebrum 

 and certain of the basal ganglia on the two sides. Fibres connect the gray 

 matter of the cerebral convolutions on the same side with each other. Fibres 

 pass from the inner surface of the gray matter of the cerebrum to the inter- 

 nal capsule, corpora striata, optic thalami and pons Varolii, to the medulla ob- 

 longata and thence to the spinal cord. The directions of these four sets of 

 fibres have been quite accurately described. 



1. Fibres connecting the Cerebrum with the Cerebellum. (A) Fibres from 

 the gray matter of the frontal lobe, in front of the anterior central convolution, 

 pass through the anterior division of the internal capsule and thence through 

 the inner portion of the outer layer of the crus cerebri (crusta) to the pons, 

 where they seem to go to the cells of the gray matter. From the pons, fibres 

 go to the lateral and posterior regions of the cerebellum on the opposite side. 

 (B) Fib'res from the occipital and temporo-sphenoidal lobes pass in the outer 

 portion of the crusta and go to the upper portion of the cerebellum, near 

 the middle lobe. This connection is probably crossed. (C) Above the 

 pyramidal tract of the crusta, is a small tract of fibres which connect the 

 caudate nucleus of the corpus striatum, through the cells of the pons, with 

 the cerebellum on the opposite side (Gowers). 



2. Fibres connecting the Two Sides of the Brain. (A) Fibres coming from 

 the inner surface of the gray matter of the cerebral convolutions pass from 

 one side to the other, through the corpus callosum, and connect the two cere- 

 bral hemispheres with each other. These are the transverse fibres of the 

 corpus callosum. (B) Fibres from the gray matter of the temporo-sphenoidal 

 lobe on either side pass through the corpora striata to the anterior com- 

 missure. These fibres connect the temporo-sphenoidal lobes, and probably 



