620 



THE VASCULAR SYSTEMS 



the circle of Willis. From its anterior part proceed the two anterior cerebrals, 

 from its antero-lateral part the middle cerebrals, and from its posterior part the 

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

 ferent 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 bra.fo , the other has been named the cortical arterial system, and its vessels 

 ramify in the pia and supply the cortex and subjacent medullary substance. These 

 two systems, although 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. In the brains of old 

 people softening is especially apt to occur in this'ill-nourished territory. 



Anterior communicating 



Anterior cerebral 



Middle cerebral 



Cl tor oid 



Posterior communicating 

 Posterior cerebral 



Superior cerebellar- 

 Basilar 

 Anterior inferior cerebellar- 



Interior auditory 

 Posterior inferior cerebellar 

 Vertebral 



Posterior spinal 



Anterior spinal 



FIG. 454. Diagram of the arterial circulation at the base of the brain. /. Antero-median group of ganglionic 

 branches. //. Postero-median group. ///. Right and left antero-lateral group. IV. Right and left postero- 

 lateral group. 



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 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. 454). 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 communi- 

 cating; (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 around the crura. 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 branches, so that by one of the small vessels 

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



