778 



NERVOUS SYSTEM OF THE HORSE 



to the tegmentum of the cerebral peduncle, the hypothalamic region, and the thalamus. After 

 the peduncles disappear under the corpora quadrigemina, they converge and many of their fibers 

 intercross, forming the decussation of the anterior peduncles. A considerable number of fibers 

 end in the nucleus ruber. Thence impulses are transmitted in two directions: first, by thalamo- 

 cortical fibers to the cerebral cortex; second, by the rubro-spinal tract through the brain stem 

 and lateral columns of the cord to the ventral horn cells. The ventro-lateral cerebellospinal 

 fasciculus (GoAvers' tract) is an ill-defined tract which connects the spinal cord with the cere- 

 bellum. Its fibers appear to be axones of cells of the dorsal columns of the cord; they pass 

 in the lateral column of the cord, become scattered in passing through the reticular formation 

 of the medulla and pons, and enter the cerebellum by way of the anterior medullary velum. 



The Fourth Ventricle 

 The fourth ventricle (Ventriculus qiiartus) is the cavity of the rhombencepha- 

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



Corpus callosum {section) Lateral ventrich 



Plexus chorioideus 



Corpus qnailrigeniiii am 



aiUerius 



Corpus quadrigeminum 

 poslerius 



Tuberculum acusticum 

 Tcsnia ventriculi quarti 



Septum pelluciduin 



Nucleus caudatus 



Thalamus {anterior 

 tubercle) 



Stria termincdis 



Corpus geniculatum 

 laterale 



Corpus genicidatum mediale 



Pedunculus cerebri 



Velum niedullare aiiterius 



Brachium conjunctivum 

 Brachium pontis 



Corpus restiforme 



Calamus scriplorius 

 Tuberculum cinereum 



Fissura mediana 



Fig. 635. — Dissection of Br.\in Stem axd B.\sal G.angli.4. of Horse; Dorsal View. 

 1, Columns of fornix (section) ; £, remnant of hippocampus; 3, tsenia thalami; .^, pineal body; o, eminentia medialis; 

 6, sulcus medianus; 7, sulcus limitans; V.III., third ventricle; V.IV., fourth ventricle. Stumps of cranial nerves are 

 indicated by Roman numerals. 



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

 in outline, elongated from before backward, and narrowest behind. It is lined 

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

 Its floor, the fossa rhomboidea, is formed by the medulla oblongata and pons 



