236 



TUB ANATOMY OF THK HORSE. 



them over. The space is continuous with the same space in the spinal 

 meninges, and contains the limpid cerebrospinal fnid. 



The PiA Mater. This is the vascular membrane of the brain. It 

 consists of delicate areolar tissue and bloodvessels. It invests the 

 brain closely, following all its surface irregularities. Behind the cerebral 

 hemispheres it sends towards the interior of the cerebrum a Avide process 

 — the velum into }x>situm ; and where the cerebellum is superposed to the 

 medulla oblongata, it forms on each side a thickened granular cord — the 

 choroid plexus of the J^th venti-icle. These will be exposed at a later stage. 



ARTERIES OF THE BRAIN (fIG. 30). 



Three vessels are conceraed in supplying blood to the encephalou, 

 viz., the basilar, internal carotid, and ophthalmic arteries. 



Fii; 



The Aktekies ok the Bkain. 

 1. Anterior branch of ceiebro-spinal artery ; 2. Basilar artery ; 3, 3. Irregular branches to medulla 

 and cerebellum ; 4. Posterior cerebellar arteries ; 5. Bifurcation of the basilar ; 0. Anterior cere- 

 bellar arteries ; 7. Posterior cerebral arteries (more numerous and sni.aller than usual); 8. Internal 

 carotid ;_ 9. Posterior communicating branch ; 10. Anterior branch of internal carotid, which divides 

 to form 11 and 12— the middle and anterior cerebral arteries ; 13. Single vessel formed by the union 

 of 11 and 12, disappearing into great longitudinal fissure ; A. Medulla oblongata ; B. Pons Varolii ; 

 C. Cerebellum ; U. Crus cerebri ; E. Corpus albicans ; F. Optic commissure ; G. Olfactory bulb ; 

 H. Cerebral hemisphere. 



The Basilar Artery is formed on the middle line of the lower face of 

 the medulla oblongata, by the union of two vessels. These are the 



