662 



NERVOUS SYSTEM OF THE HORSE 



The Fourth Ventricle 



The fourth ventricle (^''entriculus quartus) is the cavity of the rhoml^encepha- 

 lon; it communicates with the central canal of the spinal cord behind, and through 

 the aqueduct with the third ventricle in front. It is somewhat rhomboid in out- 

 line, elongated from before l)ackwar(l and narrowest behind. It is lined completely 

 by an epithelium (Ependyma) and contains a small amount of fluid. 



Its floor (Fossa rhomboidea) is formed by the medulla and pons and is marked 

 by three longitudinal furrows which converge behind. It is widest and deepest 

 a little in front of its middle. The posterior part narrows to a point at .the opening 

 of the central canal, and on account of its apjDearance in man it has been termed the 



-- Colli »i7is of fornix 



Corj>N.^ stridtiun 



~ Cliorioid ple.rNs of 

 lateral ventricle 



' Stria, terminalis 



Third venlricle 

 — Thalatnus 

 ~^ Fimbria 



Corpus genie, exterinan 

 ~~ Pineal body 



Cor]>iis genie, internum 

 '"" Corpora guadrigeniina 



Facial eminence -' 



— Anterior pedinicle of cerebellum 



— Middle pediniele of eerebelluia 



Median sulcus 



— Ijimiting suleu.'i 



— Corpus restifornie 

 - — Timid 



— Obex 



I'ubcreuluni cinereum 



— Dorso-lalcral sulcus 



— Median sulcus 



Fig. 504. — Brain Stem and Basal Ganglia of Horsf., Dorsal View. 

 The cranial nerve-roots are designated by Roman numerals. 



calamus scriptorius. The median sulcus (Sulcus mediamis) extends the entire 

 length of the floor and is deepest toward the ends. The limiting sulci (Sulci 

 limitantes) begin on either side of the opening of the central canal and extend for- 

 ward as the lateral limits of the rhomboid fossa. Just beyond the middle of the 

 fossa they expand into a shallow depression, the anterior fovea (Fovea nasalis). 

 On either side of the median sulcus and margined by the limiting sulcus is a slightly 

 rounded column, the eminentia medialis. Oi^posite the fovea this presents an 

 elongated prominence, the colliculus facialis, so named because it overlies the bend 

 formed by the fibers of origin of tlu» facial nerve. l^xtcM'nal to the limiting sulcus 

 is a long fusiform elevation, th(^ area acustica, from which a band of fibers (Strise 

 acusticie) winds over the anterior end of the restiform body to the superficial 

 origin of the cochlear nerve. 



