514 THE BLOOD-VASCULAR SYSTEM. 



These vessels divide and ramify in the substance of the pia mater, and give off 

 nutrient arteries which penetrate the cortex perpendicularly. These nutrient vessels 

 are divisible into two classes the long and short. The long or, as they are some- 

 times called, the medullary arteries pass through the gray matter to penetrate the 

 centrum ovale to the depth of about an inch and a half, without intercommunica- 

 ting otherwise than by very fine capillaries, and thus constitute so many independ- 

 ent small systems. The short vessels are confined to the cortex, where they form 

 with the long vessels a compact network in the middle zone of the gray matter, the 

 outer and inner zones being sparingly supplied with blood (Fig. 297). The vessels 

 of the cortical arterial system are not so strictly " terminal " as those of the 

 central ganglionic system, but they approach this type very closely, so that injec- 

 tion of one area from the vessel of another area, though it may be possible, is 

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

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

 the effect of producing softening in a very limited area of the cortex. 1 



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 region through which it passes. 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 termed the axillary ; and from the lower margin of the axillary space to the 

 bend of the elbow it is termed brachial ; here the single trunk terminates by 

 dividing into two branches, the radial and ulnar an arrangement precisely similar 

 to what occurs in the lower limb. 



THE SUBCLAVIAN ARTERIES (Fig. 298). 



The subclavian artery on the right side arises from the innominate artery 

 opposite the right sterno-clavicular articulation ; on the left side it arises from the 

 arch of the aorta. It follows, therefore, that these two vessels must, in the first 

 part of their course, differ in their length, their direction, and their relation with 

 neighboring parts. 



In order to facilitate the description of these vessels, more especially from a 

 surgical point of view, each subclavian artery has been divided into three parts. 

 The first portion, on the right side, passes upward and outAvard from the origin 

 of the vessel to the inner border of the Scalenus anticus. On the left side it ascends 

 nearly vertically, to gain the inner border of that muscle. The second part passes 

 outward, behind the Scalenus anticus ; and the third part passes from the outer 

 margin of that muscle, beneath the clavicle, to the outer border of the first rib, 

 where it becomes the axillary artery. The first portion of these two vessels 

 differs so much in its course and in its relation with neighboring parts that it 

 will be described separately. The second and third parts are alike on the two 

 sides. 



FIRST PART OF THE RIGHT SUBCLAVIAN ARTERY (Figs. 280, 283, 298). 



The right subclavian artery arises from the arteria innominata, opposite the 

 upper part of the right sterno-clavicular articulation, and passes upward and out- 

 ward to the inner margin of the Scalenus anticus muscle. In this part of its 

 course it ascends a little above the clavicle, the extent to which it does so varying 

 in different cases. It is covered, in front, by the integument, superficial fascia, 

 Platysma, deep fascia, the clavicular origin of the Sterno-mastoid, the Sterno- 



^ The student who desires further information on this subject is referred to Charcot's Localization 

 of Cerebral and Spinal Diseases, p. 42 et seq., whence the facts above given have been principally 

 derived. 



