316 VERTEBRAL AND BASILAR ARTERIES. 



rib. The profunda cervicis and superior intercostal frequently en- 

 croach upon the second portion, and not unfrequently a branch or 

 branches may be found proceeding from the third portion. 



The primary branches are five in number, the first three being 

 ascending, and the remaining two descending ; they are the 



Vertebral, 



{Inferior thyroid, 

 Supra-scapular, 

 Posterior scapular, 

 Superficialis cervicis. 

 Profunda cervicis, 

 Superior intercostal, 

 Internal mammary. 



The VERTEBRAL ARTERY is the first and the largest of the branches 

 of the subclavian artery ; it ascends through the foramina in the 

 transverse processes of all the cervical vertebrae, excepting the last ; 

 then winds backwards around the articulating process of the atlas ; 

 and, piercing the dura mater, enters the skull through the foramen 

 magnum. The two arteries unite at the lower border of the pons 

 Varolii, to form the basilar artery. In the foramina of the transverse 

 processes of the vertebrae the artery lies in front of the cervical nerves. 



Dr. John Davy* has observed that, when the vertebral arteries 

 differ in size, the left is generally the larger: thus in ninety-eight 

 cases he found the left vertebral the larger twenty- six times, and the 

 right only eight. In the same number of cases he found a small band 

 stretching across the cylinder of the basilar artery, near the junction 

 of the two vertebral arteries, seventeen times, and in a few instances a 

 small communicating trunk between the two vertebral arteries previ- 

 ously to their union. I have several times seen this communicating 

 branch, and have a preparation now before me in which it is ex- 

 hibited. 



The BASILAR ARTERY, so named from its position at the base of 

 the brain, runs forwards to the anterior border of the pons Varolii, 

 where it divides into four ultimate branches, two to either side. 



Brandies. The branches of the vertebral and basilar arteries are 

 the following: 



/ Lateral spinal, 

 I Posterior meningeal, 

 Vertebral, < Anterior spinal, 

 I Posterior spinal, 

 \ Inferior cerebellar, 



f Transverse, 



Basilar, \ Superior cerebellar, 

 v Posterior cerebral. 



* Edinburgh Medical and Surgical Journal, 183Q. 



