3o8 



NERVOUS SYSTEM OF VERTEBRATES. 



terminalis, causing a high ridge across the floor of the ventricle. 

 At either side it rises up in the side walls just behind the foramen 

 of Monro and bends forward over the foramen to be distributed 

 to the upper half of the mesial wall and adjacent part of the roof. 

 It also spreads back into the posterior part of the lateral lobe, 

 into the part which is usually called the occipital pole. This 

 name must not be taken to suggest any comparison with the 

 occipital cortex of the human brain and would better be avoided. 



Fig. 151. — Simple diagrams to show the history of the epistriatum in fishes and 

 amphibia. The epistriatum is represented by coarse dots adjoining the ventricle, 

 and the figures indicate how it is involved in the changes of form of the forebrain 

 and how there are developed from it the hippocampal formation and the epistriatum 

 proper of the amphibian brain. A, Petromyzon; B, Acipenser; C, Teleost; D, 

 Chimaera; E, Squalus acanthias; F, Necturus. 



The upper commissure is usually described as a true commissure 

 of the mesial and caudal regions just mentioned. It is, however, 

 not so simple, for near its point of crossing it receives fibers from 

 four other sources. First, fibers enter it from the lateral walls 

 of the hemispheres; second, fibers from the medial olfactory 

 nucleus; third, fibers from the tractus strio-thalamicus; and 

 fourth, fibers which come directly from the hypothalamus and 

 enter the commissure above the tractus strio-thalamicus. The 

 commissure also has a third place of distribution in the dorsal 



