294 SUBCLAVIAN ARTERY. 



to the olfactory and optic nerves, to the under surface of the anterior lobes, 

 the third ventricle, the corpus callosum, and the inner surface of the 

 hemispheres. The two anterior cerebral arteries are connected soon after 

 their origin by a short anastomosing trunk, the anterior communicating 

 artery. 



The Middle cerebral artery, larger than the preceding, passes outwards 

 along the fissure of Sylvius, and divides into three principal branches, 

 which supply the anterior and middle lobes of the brain, and the island 

 of Reil. Near its origin it gives off the numerous small branches which 

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



The Posterior Communicating artery, very variable in size, sometimes 

 double, and sometimes altogether absent, passes backwards and inoscu- 

 lates with the posterior cerebral, a branch of the basilar artery. Occa- 

 sionally it is so large as to take the place of the posterior cerebral 

 artery. 



The Choroidean is a small branch which is given off from the internal 

 carotid, near the origin of the posterior communicating artery, and passes 

 beneath the edge of the middle lobe of the brain to enter the descending 

 cornu of the lateral ventricle. It is distributed to the choroid plexus, and 

 to the walls of the middle cornu. 



SUBCLAVIAN ARTERY. 



The Subclavian artery, on the right side, arises from the arteria inno- 

 minata, opposite the sterno-clavicular articulation, and on the left, from 

 the arch of the aorta. The right is consequently shorter than the left, and 

 is situated nearer the anterior wall of the chest ; it is also somewhat greater 

 in diameter, from being a branch of a branch, in place of a division from 

 the main trunk. 



The course of the subclavian artery is divisible, for the sake of precision 

 and surgical observation, into three portions. The first portion of the 

 right and left arteries differs in its course and relations in correspondence 

 with the dissimilarity of origin of the respective arteries. The other two 

 portions are precisely alike on both sides. 



The first portion, on the right side, ascends obliquely outwards to the 

 inner border of the scalenus anticus. On the left side it ascends perpen- 

 dicularly to the inner border of that muscle. The second portion curves 

 outwards behind the scalenus anticus ; and the third portion passes down- 

 wards and outwards beneath the clavicle, to the lower border of the first 

 rib, where it becomes the axillary artery. 



Relations. The first portion, on the light side, is in relation, in front. 

 with the internal jugular and subclavian vein at their point of junction, 

 and is crossed by the pneumogastric nerve, cardiac nerves, and phrenic 

 nerve. Behind and beneath it is invested by the pleura, is crossed by the 

 right recurrent laryngeal nerve and vertebral vein, and is in relation with 

 the transverse process of the seventh cervical vertebra. The first portion 

 on the left side is in relation in front with the pleura, the vena innomi- 

 nata, the pneumogastric and phrenic nerves (which lie parallel to it), and 

 the left carotid artery. To its inner side is the oesophagus ; to its outer 

 side the pleura ; and behind, the thoracic duct, longus colli, and vertebra] 

 rolumn 



