486 NEUROLOGY. 



ARTERIAL CIRCULATION. 



Four large arteries, two internal carotids, and two cerebro- 

 spinal branches of the occipital arteries, convey the blood to the 

 encej)halon. An examination of the tortuous course of these 

 arteries shows how beautifully Nature has provided against injury 

 to the delicate brain-structure, by the blood impinging with too 

 great a force against its base. 



The Cerebro-spinal arteries enter the neural canal through 

 the internal foramina in the wings of the atlas, and wind round 

 the cord to its inferior surface, where they each divide into two 

 branches, one of Avhich, the anterior or cerebral branch, passes 

 forwards and joins its fellow near the middle of the medulla 

 .. ^ oblongata, to form the basi- 



'''~~y^ ^i^, lar(> artery. The posterior 



branches pass backw^ards, 

 and also coalesce to form 

 the middle spinal artery, 

 which runs along the longi- 

 tudinal fissure of the cord. 

 The Basilar artery is 

 j,^p ^yg continued forwards in the 



The encephalic arteiies. a, Anterior branch of the longitudinal furrOW On the 



right, and a', of the left carotid arteries ; & V Posterior i^-^ferior S Urface of the ponS 

 communicating branches ; c, Inosculation of the an- _ _ ^ ^ 



terior branches, d d, Inosculation of posterior com- Varolii, near the anterioF 



municating, and posterior cerebral branches of basilar i i n i_"-l'.lJ"*j 



artery: ..Basilar trunk. border of whlch it dlVldeS 



into two branches, the pos- 

 terior cerebrals. In its course the basilar artery gives off — 1st, 

 Several small branches, which penetrate the surface of the medulla 

 oblongata and pons Varolii ; 2m?, The p>osterior cerebellars, right 

 and left, which, like the terminal branches, are given off at right 

 angles behind the posterior border of the pons. They are carried 

 outwards, ascending over the pons, and then, inflected backwards, 

 are distributed over the lateral and posterior parts of the cere- 

 bellum. Srd, The anterior cerebellar arteries, two or three on 

 each side, the principal being given off just in front of the pons, 

 on the outer side of which it ascends in an outw^ard and slightly 

 backward direction, to be distributed to the anterior surface of 

 the cerebellum. 



The terminal branches, the Posterior cerebral arteries, are 

 the largest, and form the posterior border of that peculiar arterial 



