THE CENTRAL NERVOUS SYSTEM 



727 



answer, and the answers to some of which must for ever remain 

 hidden from us. 



Functions of the Upper Part of the Central Stem and Basal 

 Ganglia. The function of the pons is sufficiently indicated by its 

 name. The grey matter so plentifully scattered, especially in its 

 ventral portion, may exercise a not unimportant influence on the 

 impulses that traverse it. But on the whole its main office is to 

 provide a bridge along which impulses may travel between other 

 portions of the nervous system. We have already seen that many 

 of its transverse fibres are the cerebellar segments of commissural 

 arcs interrupted by pontine grey matter, and continued by fibres of 



Corpus striatum 



Anterior pillar of the 

 fornix 



Optic thalamus 

 Third ventricle 



FIG. 260. HORIZONTAL SECTION THROUGH BRAIN TO SHOW THE BASAL 

 GANGLIA AND THIRD VENTRICLE (HUMAN). 



the crura cerebri, internal capsule and corona radiata to the pre- 

 frontal, temporal and occipital portions of the cerebral cortex (p. 690). 



The posterior corpora quadrigemina (testes) and internal geniculate 

 bodies are connected with the cochlear division of the auditory 

 nerves, and therefore have some relation to the sense of hearing. 

 Stimulation of the testes causes a peculiar cry, and the pupils dilate. 



The anterior corpora quadrigemina (nates) and the lateral corpora 

 geniculata are connected with the optic tracts. Their development 

 is arrested after extirpation of the eyeball in young animals, and 

 they may therefore be assumed to be concerned in vision, athough 

 the size of their homologues, the optic lobes or corpora bigemina, in 

 animals below the rank of mammals (birds, reptiles, amphibians), 

 does not seem to be related to the development of the organs of 

 sight. The Proteus and the Hag-fish, e.g., have large optic lobes, 

 rudimentary eyes and optic tracts. The optic nerve, the anterior 



