THE BLOOD-VESSELS OF THE BRAIN. 



513 



posterior cerebrals. Each of these principal arteries gives origin to two very 

 different systems of secondary vessels. One of these systems has been named the 

 central ganglionic system, and the vessels belonging to it supply the central ganglia 

 of the brain ; the other has been named the cortical arterial system, and its vessels 

 ramify in the pia mater and supply the cortex and subjacent medullary matter. 

 These two systems, though they have a common origin, do not communicate at any 

 point of their peripheral distribution, and are entirely independent of each other. 

 Though some of the arteries of the cortical system approach, at their terminations, 

 the regions supplied by the central ganglionic system, no communication between 

 the two sets of vessels takes place, and there is between the parts supplied by 

 the two systems a borderland of diminished nutritive activity, where, it is said, 

 softening is especially liable GO occur in the brains of old people. 



The Central Ganglionic System. All the vessels belonging to this system are 

 given off from the circle of Willis or from the vessels immediately after their origin 



mater, b. Network with more compact, polygonal meshes, situated in the cortex, c. Transitional network with 

 wider meshes, d. Capillary network in the white matter. 



from it, so that if a circle is drawn at a distance of about an inch from the circle 

 of Willis, it will include the origin of all the arteries belonging to this system (Fig. 

 296). The vessels of this system form six principal groups : (I.) the antero-median 

 group, derived from the anterior cerebrals and anterior communicating ; (II.) the 

 postero-median group, from the posterior cerebrals and posterior communicating ; 

 (III.) the right and left antero-lateral group, from the middle cerebrals : and (IV.) 

 the right and left postero-lateral group, from the posterior cerebrals, after they have 

 wound round the crura cerebri. The vessels belonging to this system are larger 

 than those of the cortical system, and are what Cohnheim has termed " terminal " 

 arteries ; that is to say, vessels which from their origin to their termination neither 

 supply nor receive any anastomotic branch, so that by one of the small vessels 

 only a limited area of the central ganglia can be injected ; and the injection cannot 

 be driven beyond the area of the part supplied by the particular vessel which is the 

 subject of the experiment. 



The Cortical Arterial System. The vessels forming this system are the terminal 

 branches of the anterior, middle, and posterior cerebral arteries, described above. 



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