790 NERVOUS SYSTEM OF THE HORSE 
laterales).1_ The ventral surface has the reverse configuration, and presents trans- 
verse ridges and grooves. It forms the roof of the lateral ventricles, and the 
septum pellucidum is attached to it medially. The fibers of the corpus callosum 
(with the exception of the longitudinal strie) run transversely and spread out 
laterally in all directions in the central white matter of the hemispheres to the cor- 
tex, forming the radiation of the corpus callosum (Radiatio corporis callosi). 
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, 
two columns, and two crura. The 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 dorsal surface gives 
Interventricular foramen 
Anterior commissure 
Optic Optic tract 
chiasm 
Fia. 643.—Cross-SECTION OF BRAIN OF Horse, AsoutT NATURAL SIZE, 
Section passes through optic chiasm, and is viewed from in front. 1, Longitudinal fissure; 2, septum pellu- 
cidum; 3, columns of fornix; 4, lateral ventricle; 5, chorioid plexus; 6, corpus medullare (central white matter) of 
hemisphere; 7, caudate nucleus; 8, lenticular nucleus; 9, internal capsule; /0, external capsule; 11, insula. 
attachment medially 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 the inner boundary of the interventricular foramen. 
The columns (Column fornicis) (Fig. 643)? are two slender round bundles which 
emerge from the body in front of the interventricular foramen and diverge 
slightly as they curve ventrally 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 Vieq d’Azyr). Others pass to 
the cerebral peduncle. A portion of the fibers cross to the opposite thalamus and cerebral 
peduncle. 
The crura (Crura fornicis)* are much larger bands which diverge widely from 
1 Tt is generally believed that these constitute an olfactory path. 
? Also known as the anterior pillars. 3 Also termed the posterior pillars. 
