264 RIGHT AND LEFT SUBCLAVIAN ARTERIES. 



ana. It runs outwards nearly in the direction of the fossa Sylvii, 

 which separates the anterior from the middle lohes of the cere- 

 brum. In its course it divides and subdivides into numerous 

 branches, which are spread upon the Pia Mater, and finally 

 enter the surface of the brain in a very minute state. 



The internal carotid then terminates in a branch, which is 

 smaller than the last mentioned, and from its situation is called 

 the Anterior Artery of the Brain, or Arteria Callosa. This 

 vessel first inclines towards its fellow on the opposite side, and 

 after approaching within half an inch of it, forms another curve, 

 and runs forward to the anterior part of the brain, dividing 

 itself gradually into two branches, which pass in several 

 directions. 



Where these anterior arteries are nearest to each other, a small 

 transverse branch, which passes at right angles, connects them 

 together. This branch is called communicans anterior, and com- 

 pletes the anterior part of the Circle of Willis. 



It crosses immediately before the sella turcica and pituitary 

 gland, and sends off branches which pass to the third ventricle, 

 to the fornix and septum lucidum, and also to the pia mater. 



The Anterior Arteries of the brain also send off branches to 

 the optic and olfactory nerves ; to the opposite surfaces of the 

 two hemispheres on each side of the falx, to their inferior sur- 

 faces, and to the corpus callosum. 



They have likewise some branches which anastomose with 

 those of the middle artery of the brain, and of the vertebral 

 artery. 



The Subdavian Arteries. 



The Right Subdavian may be considered as the continuation 

 of the arteria innominata. This last mentioned artery, after 

 leaving the aorta, forms a curve or arch, which extends obliquely 

 backwards and outwards, over the first rib to the axilla, crossing 

 the trachea in its course. At the distance of an inch and a 

 quarter or an inch and a half from its origin, it sends off the 

 right carotid, and then, assuming the name of Right Subdavian, 

 continues in the above stated direction. 



