VESSELS OF THE BEAIN AND CORD. 103 



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

 lamencephalon, where they again divide; one division^ arteria 

 lobi henmjjhaerici inferior externa (Schobl), continues fonvards along 

 the outer sui-face of the cerebral hemisphere and of the olfactory 

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

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

 wards. The vessels of the two sides communicate A\ith each other 

 by means of delicate transverse vessels [Arteriae communicantes ante- 

 riores). The second division, arteria lobi hemispJiaerici superior in- 

 terna (Schobl), of the ramus anterior com-ses on the thalamencephalon 

 to the dorsal sui-face, gives a large branch to the choroid plexus of 

 the fourth ventricle, and runs forwards in the dorsal longitudinal 

 iissm-e ; it supplies vessels to all the neighbom-ing parts. 



The rami jjosteriores converge as they course backwards, and ulti- 

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

 median line of the under sm-face of the spinal cord as the arteria 

 spinalis anterior. The ramus posterior gives off, in its course, many 

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

 either side, one of which, the arteria lobi opdici (Schobl), is distributed 

 to the oj)tic lobes, while the other passes to the pituitary body. 



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

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

 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 pjosteriores, and from the arteria basi- 

 laris ; 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 pjars commissuralis a large branch may 

 be traced from the ramus posterior on either side iip wards into the 

 cerebellum almost to its vipper 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 vascidar than the white ; the vessels of 

 the latter are chiefly arranged radially to the sm-face, and run in 

 courses which are more or less straight; the vessels of the g'rey 

 matter are more irregular and sinuous. 



The Arteria spinalis anterior courses along the whole length of 

 the spinal cord, giving off lateral branches and commmiicating with 



M 2 



