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ANATOMY. 



FIG. 57. 



Middle Cerebral, in the fissure of Sylvius ; divides into 3 branches, anterior, 



median, and posterior. 



Anterior Choroid, to the choroid plexus, corpus fimbriatum, etc. 

 Posterior Communicating, anastomoses with the posterior cerebral, a branch 



of the basilar. 



What is the Circle of Willis ? An anastomosis at the base of the brain, 

 between the branches of the internal carotid and vertebral arteries, to equalize 

 the cerebral circulation. The 2 Vertebral arteries join to form the Basilar, 

 which ends in 2 Posterior Cerebral. These are connected with the Internal 

 Carotid by the 2 Posterior Communicating. The circle is completed by the 

 connection of the 2 Anterior Cerebral branches of the internal carotid through 

 the short Anterior Communicating artery. 



Describe the Subclavian. It arises on the right side from the innominate, 



on the left side from the arch of the aorta, 

 and is divided into 3 portions by the 

 scalenus anticus, which crosses it just ex- 

 ternal to the origin of the thyroid axis, 

 viz. the parts internal, behind, and ex- 

 ternal to that muscle. At the outer border 

 of the ist rib, the subclavian becomes the 

 axillary artery. Its upper border is a little 

 above the clavicle, and it is separated from 

 the subclavian vein by the scalenus anticus 

 at its origin from the first rib. Its branches 

 are all given off from its first portion, ex- 

 cept the Superior Intercostal, which on 

 the right side arises from the second por- 

 tion. 



Vertebral? passing up the neck, through 

 the foramina in the transverse pro- 

 cesses of six cervical vertebrae, and enters the skull by the foramen 

 magnum, where it joins its fellow to form the Basilar Artery. Its 

 branches are 



Lateral Spinal Branches. Anterior Spinal. 



Muscular Branches. Posterior Spinal. 



Posterior Meningeal. Inferior Cerebellar. 



The Basilar, formed by the junction of the vertebrals, gives off on each 

 side a transverse, anterior, and superior cerebellar, and ends in the two 

 posterior cerebral. (See Circle of Willis, above.) 



