Mammalia: Nervous System 



•TECTUM OPTICUM 



'CEREBELLUM 



Fig. 529. Diagram illustrating the connections of optic nerve-fibers in (A) a 

 fish, (B) a reptile, and (C) a mammal. The definitive centers of vision lie in the 

 occipital lobes of the cerebral hemispheres. Some primitive centers in the optic 

 lobes persist in mammals as reflex centers. (After Monakow. Courtesy, Neal and 

 Rand: "Comparative Anatomy," Philadelphia, The Blakiston Company.) 



The roof of the mesencephalon becomes thickened to form lobes 

 which are more or less important as the seat of primary visual cen- 

 ters (Figs. 522, 528). In vertebrates other than mammals, a single pair 

 of optic lobes (corpora bigemina) are the chief seat of the primary 

 visual centers. In mammals two pairs of lobes (corpora quadri- 

 gemina) appear in the roof of the mesencephalon. Those of the an- 

 terior pair are visual centers, but those of the posterior and smaller 



