VESSELS OF THE BEAIX AND CORD. 103 



the surface of the brain as far as the anterior portion of the tha- 

 lamencephalon. where they again divide; one division, artena 

 lobi /temixjJiaeriri inferior externa (Schobl), continues forwards along 

 the outer surface of the cerebral hemisphere and of the olfactory 

 lobe as far as the olfactory bulb, where it may still be distinctly 

 seen ; it gives off branches to the adjacent parts in its course for- 

 wards. The vessels of the two sides communicate with each other 

 by means of delicate transverse vessels (Arteriae communicant es ante- 

 riore*). The second division, arteria lobi Jiemizphaerici superior in- 

 terna (Schobl), of the ramm anterior courses on the thalamencephalon 

 to the dorsal surface, gives a large branch to the choroid plexus of 

 the fourth ventricle, and runs forwards in the dorsal longitudinal 

 fissure ; it supplies vessels to all the neighbouring parts. 



The rami posterior** converge as they course backwards, and ulti- 

 mately unite to form an arteria baxilarix, which is continued in the 

 median line of the under surface of the spinal cord as the artena 

 xpinali* anterior. The ram** posterior gives off, in its course, many 

 small vessels to the neighbouring parts, and two larger vessels on 

 either side, one of which, the artena lobi opt id (Schobl), is distributed 

 to the optic lobes, while the other passes to the pit\iitary body. 



The branches of these vessels form a network in the pia mater, 

 from which the nervous tissue is supplied ; they also send numerous 

 branches directly into the brain and cord, and these have a similar ar- 

 rangement for all parts of the brain with the exception of the cerebral 

 hemispheres and olfactory lobes ; more or less vertical branches arise 

 from the posterior parts of the upper borders of the rami anteriores, 

 from the whole of the rami posteriores, and from the artena basi- 

 -. these course upwards from their place of origin into the corre- 

 sponding part of the brain, give off a few branches in the white 

 matter, and then branch freely, and at somewhat sharp angles, 

 in the grey matter. In the _/;/# commissuralis a large branch may 

 be traced from the rannis posterior on either side upwards into the 

 cerebellum almost to its upper border. The vessels of the cerebral 

 hemispheres and olfactory lobes seem to possess no other definite 

 arrangement than that described above. The grey matter seems, 

 on the whole, to be more vascular than the white ; the vessels of 

 the latter are chiefly arranged radially to the surface, and rim in 

 courses which are more or less straight ; the vessels of the grey 

 matter are more irregular and sinuous. 



The Arteria fyhiatiz anterior courses along the whole length of 

 the spinal cord, giving off lateral branches and communicating with 



.u. 2 



