108 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



over the gray surface of the quadrigeminal body (stratum zonale) 

 and end in a fine net-work, which apparently takes its origin in 

 the numerous delicate cells which are found in this locality. 



The posterior quadrigeminal body appears also to stand in 

 some relation with the optic tract, but it is very improbable that 

 it contains fibres which are of any use in the visual act. Its 

 brachium originates in the corpus geniculatum mediale and in 

 the hitherto unmentioned commissura inferior (Gudden's com- 

 missure), which passes along with the optic tract to the posterior 

 angle of the chiasm. (See Fig. G6.) It may also, perhaps, con- 

 tain fibres from the temporal lobe. The extraordinary develop- 

 ment of the posterior quadrigeminal body in cetaceans, and the 

 huge bands of fibres which pass from it to the nucleus of the 

 acoustic nerve, make it probable (Spitzka) that this ganglion 

 stands in some relation to the sense of hearing. The results of 

 experiments undertaken to elucidate the point seem to agree 

 with this. After destruction of the acoustic nerve the posterior 

 quadrigeminal body is said to become somewhat atrophied 

 (Baginski). It seems to me, however, that this special point 

 needs further investigation. 



Viewed laterally the relations of the quadrigeminal brachia 

 to the ganglia and the optic tract are plainly seen ; also the 

 situation of the corpora geniculata; the corpus geniculatum 

 mediale lying close to the posterior brachium, and the corpus 

 geniculatum laterale seeming to be thrust between the pulvinar 

 and the optic tract. The corpus geniculatum laterale was men- 

 tioned when we were describing the thalamus. From the latter 

 ganglion fibres pass to the optic tract aside from those which 

 issue from the pulvinar and the stratum zonale. The optic 

 fibres, from the anterior quadrigeminal body, have alretidy been 

 described. They run their course, to a great extent, in its 

 brachium. Besides these the nerve receives roots from the 

 region of the corpus subthalamicum, and from the gray matter 

 in the vicinity of the infundibulum (basal optic root). Compare 

 Fig. 66. 



