468 ARTERIES. 



The middle cerebral artery, the largest branch of the internal carotid, passes 

 obliquely outwards along the fissure of Sylvius, within which it divides into 

 three branches ; an interior, which supplies the pia mater, investing the surface 

 of the anterior lobe; a posterior, which supplies the middle lobe; and a median 

 branch, which supplies the small lobe at the outer extremity of the Sylvian fis- 

 sure. Near its origin, this vessel gives off numerous small branches, which 

 enter the substantia perforata, to be distributed to the corpus striatum. 



The posterior communicating artery arises from the back part of the internal 

 carotid, runs directly backwards, and anastomoses with the posterior cerebral, a 

 branch of the basilar. This artery varies considerably in size, being sometimes 

 small, and occasionally so large that the posterior cerebral may be considered 

 as arising from the internal carotid rather than from the basilar. It is frequently 

 larger on one side than on the other side. 



The anterior choroid is a small but constant branch which arises from the back 

 part of the internal carotid, near the posterior communicating artery. Passing 

 backwards and outwards, it enters the descending horn of the lateral ventricle, 

 beneath the edge of the middle lobe of the brain. It is distributed to the hip- 

 pocampus major, corpus fimbriatum, and choroid plexus. 



AETERIES OF THE UPPER EXTREMITY. 



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

 from its commencement, as far as 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, as far as 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 ter- 

 minates by dividing into two branches, the Radial and Ulnar, an arrangement 

 precisely similar to what occurs in the lower limb. 



SUBCLAVIAN ARTERIES. 



The Subclavian Artery on the right side arises from the arteria innominata, 

 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 in their re- 

 lation with neighboring parts. 



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

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

 The first portion, on the right side, ascends obliquely outwards, from the origin 

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

 ascends perpendicularly, to gain the inner border of that muscle. The second 

 part passes outwards, behind the Scalenus Anticus ; and the third part passes 

 from the outer margin of that muscle, beneath the clavicle, to the lower border 

 of the first rib, where it becomes the axillary artery. The first portions of these 

 two vessels differ so much in their course, and in their relation with neighboring 

 parts, that they will be described separately. The second and- third parts are 

 precisely alike on both sides. 



FIRST PART OF THE RIGHT SUBCLAVIAN ARTERY. (Figs. 272, 274.) 



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

 right sterno-clavicular articulation, passes upwards and outwards across the 

 root of the neck, and terminates at the inner margin of the Scalenus Anticus 

 muscle. In this part of its course, it ascends a little above the clavicle, the ex- 

 tent 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-mastoicl, the Sterno-hyoid, and Sterno-thyroid muscles, and another 



