THE CEREBRAL HEMISPHERES 



673 



The fornix is a bilateral structure composed of white fibers which arch chiefly 

 over the thalamus and the third ventricle. It is described as consisting of a body 

 and two pairs of i:)illars. Th(> body (Corpus fornicis) is formed by the fusion of the 

 two arches of which the fornix is composed. It is triangular and overlies the an- 

 terior parts of the thalami and the third ventricle. The upper surface gives 

 attachment to the septum pellucidum and on either side forms part of the floor of 

 the lateral ventricle. The lateral border is related to the chorioid plexus of the 

 lateral ventricle and forms tiie inner boundary of the interventricular foramen. 

 The anterior pillars or columns (Colummie fornicis) (Fig. 512) are two slender 

 round bundles which emerge from the body in front of the interventricular foramen 



'Olfactory bulb 



-'-' Cortex cerebri 



^ Corpus medullare 



, Caudate nucleus 



-Chorioid plexus 



Fornix 



' - ^.-^--j - -Hippocampus 



V 



Fig. 511. — Brain of Horse, with Lateral Ventricles Opened by Removal of Upper Part of Cerebral, 



Hemispheres. 



and diverge slightly as they curve downward and backward to the mammillary 

 body. 



From the mammillary body the greater part of these fornix fibers are continued to the 

 thalamus by the thalamo-mammillary fasciculus (or bundle of Vicq d'Azyr). Others pass to 

 the cerebral peduncle. A portion of the fibers cross to the opposite thalamus and cerebral 

 peduncle. 



The posterior pillars (Crura fornicis) are much larger bands which diverge 



widely from the posterior angles of the body. Each curves outward and backward 



over the thalamus (from which it is separated by the tela chorioidea) and is chiefly 



continued as the fimbria along the concave border of the hippocampus. The pillars 



43 



