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 cerebrospinal fluid. 



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

 consists of delicate areolar tissue and blood vessels. 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. 



The Arteries of the Brain 



1. Anterior branch of cerebrospinal 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) ; 8. Internal 

 carotid ; 9. Posterior communicating branch ; 10. Anterior brar ch of internal carotid, \vl>ich divides 

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

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

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

 H. Cerebral hemisphere. 



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

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

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

 exposed at a later stage. 



