THE SU SCLAV I AN ARTERY 575 



The Ganglionic System. All the vessels of this system are given off from the 

 arterial circle of Willis, or from the vessels close to it. They form six principal 

 groups: (I) the antero-medial group, derived from the anterior cerebrals and anterior 

 communicating; (II) the postero-medial group, from the posterior cerebrals and 

 posterior communicating; (III and IV) the right and left antero-lateral groups, 

 from the middle cerebrals; and (V and VI) the right and left postero-lateral 

 groups, from the posterior cerebrals, after they have wound around the cerebral 

 peduncles. The vessels of this system are larger than those of the cortical system, 

 and are what Cohnheim designated terminal arteries that is to say, vessels which 

 from their origin to their termination neither supply nor receive any anastomotic 

 branch, so that, through any one of the vessels only a limited area of the thalamus 

 or corpus striatum 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. They divide 

 and ramify in the substance of the pia mater, and give off branches which penetrate 

 the brain cortex, perpendicularly. These branches are divisible into two classes, 

 long and short. The long, or medullary arteries, pass through the gray substance 

 and penetrate the subjacent white substance to the depth of 3 or 4 cm., without 

 intercommunicating otherwise than by very fine capillaries, and thus constitute 

 so many independent small systems. The short vessels are confined to the cortex, 

 where they form with the long vessels a compact net-work in the middle zone 

 of the gray substance, the outer and inner zones being sparingly supplied with 

 blood. The vessels of the cortical arterial system are not so strictly "terminal" 

 as those of the ganglionic system, but they approach this type very closely, so 

 that injection of one area from the vessel of another area, though possible, is 

 frequently very difficult, and is only effected through vessels of small caliber. As 

 a result of this, obstruction of one of the main branches, or its divisions, may have 

 ic effect of producing softening in a limited area of the cortex. 



THE ARTERIES OF THE UPPER EXTREMITY. 



The artery which supplies the upper extremity continues as a single trunk 

 from its commencement down to the elbow; but different portions of it have received 

 different names, according to the regions through which they pass. That part 

 of the vessel which extends from its origin to the outer border of the first rib is 

 termed the subclavian; beyond this point to the lower border of the axilla it is 

 named the axillary; and from the lower margin of the axillary space to the bend 

 of the elbow it is termed brachial; here the trunk ends by dividing into two branches 

 the radial and ulnar. 



THE SUBCLAVIAN ARTERY (A. SUBCLAVIA) (Fig. 520). 



On the right side the subclavian artery arises from the innominate artery behind 

 the right sternoclavicular articulation: on the left side it springs from the arch 

 of the aorta. The two vessels, therefore, in the first part of their course, differ 

 in length, direction, and relation with neighboring structures. 



In order to facilitate the description, each subclavian artery is divided into 

 three parts. The first portion extends from the origin of the vessel to the medial 

 border of the Scalenus anterior; the second lies behind this muscle; and the third 

 extends from the lateral margin of the muscle to the outer border of the first rib, 

 where it becomes the axillary artery. The first portions of the two vessels require 



separate descriptions ; the second and third parts of the two arteries are practically 

 1*1 

 alike- 





