CENTERS OF CORRELATION. 263 



it and the tectum opticum. In man the anterior corpus quad- 

 rigeminum is small and poorly developed as compared with that 

 of lower animals. The descending tract from it is relatively 

 small and represents only a part of the tractus tecto-bulbaris of 

 lower vertebrates. The bundles of the two sides descend over the 

 central gray of the midbrain and form a decussation in its ventral 

 wall called by Forel the " fountain-like" decussation. As the 

 tracts pass on toward the medulla oblongata they give collaterals 

 and terminals to the nuclei of the eye muscle nerves. This is 

 the chief connection of the tract going out from the anterior quad- 

 rigeminum and it shows that the chief function of that nucleus 

 is to direct eye muscle reflexes to visual stimuli. The existence 

 of fibers from the anterior quadrigemina to the cerebral cortex has 

 not been clearly demonstrated and the complete loss of the ante- 

 rior quadrigemina does not affect light or color vision. 



The corpus geniculatum, on the other hand, sends a large tract 

 to the occipital region of the cortex and the geniculatum is the 

 chief intermediate center in visual perception. The connection of 

 the geniculatum and pulvinar with the occipital cortex is clearly 

 shown by the secondary degeneration of these nuclei after destruc- 

 tion of the visual cortical area. The tract has been followed 

 clearly in animals by the method of Golgi (Cajal) and in the new- 

 born babe the tract from the geniculatum to the cortex is medul- 

 lated while adjacent tracts are not, so that Weigert staining gives 

 a clear picture of this conduction path (Flechsig). There is evi- 

 dence that in lower vertebrates fibers pass from the tectum 

 opticum and the geniculatum to the forebrain and it is probable 

 that this tract was one of the first to stimulate the development 

 of the neopallium. Little is certainly known of the relations of 

 the geniculatum in lower vertebrates, although connections with 

 various parts of the brain have been described (Catois, Edinger). 



The existence of the corpus geniculatum laterale in selachians 

 shows that it is far from being a new or phylogenetically young 

 optic center. It is equally true, however, that it does not become 

 important relative to the tectum opticum until the cerebral hemi- 

 spheres are developed. Through the vertebrate series there has 

 been a gradual shifting cephalad of the endings of optic tract 



