538 



THE EYE IN EVOLUTION 



cells reinforced by the choroidal plexus, is given off the pineal and in some 

 Vertebrates (Cyclostomes, some Fish and Reptiles) the parietal organs ; 

 in some lower Vertebrates these have an optical function but in the higher 

 types the pineal body has only a glandular function. ^ From the floor a 

 ventral process, the infundibulum, grows in front of the anterior extremity 

 of the notochord to meet a diverticulum from the pharynx to form the pitui- 

 tary gland (or hypophysis), and with it are associated a number of nuclei 

 of neuro-secretory cells which not only control the potent endocrine products 



A'rostriatvim 



Thalanin-striatal tract 



Thalamus 



Ventral thalamic nucleus 



TECTUM 



Nerve I -"~ 



Lat. geniculate body 

 Brachium tecti 



Torus semicircularis 

 Ganglion islhmi 



Lat. lemniscus 



VI n. Cochlear 



1 Vni. Vestib. 



Nerve V 



Post, root ganglia 



Fig. 713. — -The Visual Pathways in a Typical Reptile. 



of the pituitary but, through it, exercise a governing influence over most 

 of the endocrine system. ^ 



The OPTIC THALAMUS when fully developed is a region of great integrative 

 importance. Its more dorsal nuclei are concerned with widespread somatic 

 sensory functions, the special senses and associative sensory functions. In 

 Vertebrates below Mammalia it is the part of the brain which is responsible 

 for the affective appreciation of experience and therefore, in the last resort, 

 it determines behaviour ; the cerebral hemispheres merely form the receptive 

 apparatvis for olfactory impressions. In Mammals it is the principal end- 

 station tor all the sensory systems of the body with the exception of the 

 olfactorv ojections which proceed directly to the cerebral cortex. In these 



p. 716. 



p. 558. 



