670 



NERVOUS SYSTEM OF THE HORSE 



is therefore continuous with the fimbria. The two liippocampi are connected at 

 their highest parts by transverse fibers which constitute the hippocampal commis- 

 sure. 



The interval between the hippocampus and fimbria on the one hand and the 

 brain-stem on the other is a lateral continuation of the great transverse fissure of 

 the brain, and is termed the chorioid fissure. It is occupied by a fold of pia mater, 

 the tela chorioidea of the third ventricle, or velum interpositum. This fold is 

 triangular in outline and its apex reaches to the interventricular foramen. Its base 

 is continuous at the transverse fissure with the pia which covers the surface of the 

 brain. Its middle part lies over the epithelial roof of the third ventricle, as has 



Gyrus fornicatus 



Transverse 



Cnlloso-niar- 

 ginal fissure 



Marginal fissure 



- Entoinarginal fissure 



Anterior coni- 



missure Lamina Chiasma 

 terminahs oplicum 



1 commissure • a , ■ v .l 

 , • Anterior tourth 



Pituitary Cerebral medul- ventricle 



body 



aqueduct lary 

 velum 



Fig. 508. — Median Section of Brain of Horse. 

 The iiieinbrane.s and vessels are removed. C, Central white matter (corpus meduUare) of cerebellum; 

 P.O., cerebral petluncle; C'.f/., corpora quadrigeinina; P, pineal body; Th., thalamus; V .III., third ventricle; 

 r, optic recess; r', infundibular recess; Cm., mammillary body; s, subcallosal gyrus; A.p., area parolfactoria; 

 G, genu of corpus callosum; S, splenium of same; 1, callosal sulcus; 2, interventricular foramen; 3, olfactory 

 bulb. The cerebral lobe of the jjituitary body is distinguished by its lighter color. 



been seen (Fig. 506). The lateral })orders will be seen on the floor of the lateral 

 ventricles, where they form thick rounded bands containing convolutions of 

 blood-vessels, known as the chorioid plexuses of the lateral ventricles (Fig. 511). 



When the tela is pulled out one may easily get the impression that the lateral ventricle 

 communicates with the exterior by means of the chorioid fissure. Such is not the case, since the 

 chorioid plexus is covered by the epithelial lining of the ventricle, which has been torn away. 



The rhinencephalon or olfactory part of the brain comprises the olfactory 

 bulb, peduncle and tracts or roots, the trigonum olfactorium, the area parolfactoria, 

 and the pyriform lobe.' 



' From the morphological point of view other structures should be included, but in descriptive 

 anatomy it is usual to limit the applifuition of the term to the parts enumerated above. 



