THE CEKEBRO-SPINAL NERVOUS SYSTEM. 523 



spoken of situated in the posterior frontal and anterior parietal regions. 

 Some of the fibres pass into the optic thalamus. The fibres of the fifth 

 nerve join the tegmentum, and so in the internal capsule are included 

 with the other sensory fibres. This is also probably the case with the 

 other nerves of special sense, smell, vision, and hearing. 



Cerebro-cerebellar fibres. The tracts of fibres connecting the cere- 

 bellum with the cerebrum are in all probability at least three in number. 

 (a. ) Fibres situated in the crusta to the inside of the pyramidal fibres 

 (Fig. 360). These pass upwards in the anterior limb of the internal 

 capsule and proceed into the anterior frontal lobes. In the other direc- 

 tion they descend to the pons, and appear to end in the gray matter 

 within it. But it is very likely that from this gray matter fibres pro- 

 ceed, to the lateral and posterior parts of the opposite side of the 

 cerebellum. As the fibres degenerate downwards they conduct in the 

 same direction, but are arrested at the pons, where they are interrupted 

 by gray matter. (#.) Fibres which in the crusta are situated outside 

 the pyramidal tract do not enter the internal capsule, but at once pro- 

 ceed to the occipital and temporo-sphenoidal lobes. These fibres pro- 

 ceed downwards to the cerebellum, being interrupted in the pons, and 

 from thence proceed to the upper surface of the opposite side of the 

 cerebellum near the middle lobe, (c.) The third tract is situated (Fig. 

 359, i, F) beneath the pyramidal fibres and above the locus niger. The 

 fibres pass from the corpus striatum chiefly from the caudate nucleus to 

 the pons and thence to the cerebellum. 



Functions of the Corpora Striata. The idea that the corpora striata 

 are concerned in the transmission of motor impulses, or that they are 

 the great motor ganglia at the base of the brain, rests upon insufficient 

 evidence. It has been already incidentally mentioned that lesions of the 

 corpora striata produce hemiplegia only because of the pressure effects 

 they exercise upon the internal capsule close by. 



The caudate nucleus is connected with the opposite side of the cere- 

 bellum by fibres which conduct downwards, and the lenticular nucleus 

 is connected with the cerebellum by fibres from the tegmentum and supe- 

 rior cerebellar peduncles which conduct upwards. It is suggested that the 

 corpora striata are central organs analogous to the cerebral cortex itself. 

 " The analogy to those parts of the cortex that are connected with the 

 cerebellum is rendered still greater by the fact that a lesion, even an ex- 

 tensive lesion, may exist in either the caudate or lenticular nucleus, and 

 so long as it does not interfere with the functions of the motor or sen- 

 sory parts of the internal capsules it causes no persistent symptoms/' 

 (Growers.) 



Functions of the optic thalami. That the optic thalami are the great 

 sensory centres at the base of the brain which was a view held by many 

 until recently does not seem to be based upon sufficiently accurate ob- 



