242 THE ANATOMY OF THE HORSE. 



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

 spinal meninges, and contains the limpid cerehro-spinal fluid. 



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 cere- 

 bral hemispheres it sends towards the interior of the cerebrum a wide 



Fig. 34. 

 Thi! Arteries of the Brain. 



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

 and cerebellum ; 4. Posterior cerebellar arteries ; 5. Bifurcation of the basilar ; 6. Anterior cere- 

 bellar arteries ; 7, Posterior cerebral arteries (more numerous and smaller than usual) ; S. 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 tl)e union 

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

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

 H. Cerebral hemisphere. 



process — the velum inierposiium ; and where the cerebellum is super- 

 posed to the medulla oblongata, it forms on each side a thickened 

 granular cord — the choroid plexus of the Jfth ventricle. These "will be 

 exposed at a later stage. 



