THE HEART AND VASCULAR SYSTEM. 187 



1. The vertebral artery passes upward, enters the foramen 

 in the transverse process of the sixth cervical vertebra, and 

 ascends through the foramina until it reaches the atlas, when 

 it runs backward, pierces the posterior occipito-atloid ligament 

 and dura mater to enter the skull through the foramen magnum. 

 After entering the cranium it passes forward to the lower border 

 of the pons Varolii, where it unites with its fellow of the oppo- 

 site side to form the basilar artery. Its branches are 



Cervical branches : 



Lateral spinal, supply the spinal cord and its membranes, entering 

 the spinal canal through the intervertebral foramina; 

 Muscular, supply the deep muscles of the neck. 



Cranial branches: 



Posterior meningeal, supply the falx cerebelli; 



Anterior spinal, supplies the cord; uniting with branches from the 

 inferior thyroid, intercostals, and lateral sacral, descend to the cauda 

 equina ; 



Posterior spinal, descends in the same manner as the anterior; 



Posterior inferior cerebellar, supplies the inferior surface of the 

 cerebellum and the choroid plexus of the fourth ventricle. 



The branches of the basilar artery are : 



Transverse, to the pons Varolii and inferior surface of the cere- 

 bellum ; 



Anterior inferior cerebellar, a branch of the transverse; 



Superior cerebellar, supplies pia mater, pineal gland, and velum 

 interpositum ; 



Posterior cerebral, to posterior lobes of cerebrum and choroid 

 plexus. 



2. The thyroid axis consists of three branches the inferior 

 thyroid, the suprascapular, and the transversalis colli. 



3. The inferior thyroid artery is distributed to the thyroid 

 gland, its branches being : 



Laryngeal, to muscles and mucous membrane of larynx; 



Tracheal, to the trachea, anastomosing with the bronchial arteries; 



(Esophageal, to oesophagus; 



Ascending cervical, supplies the spinal cord and membranes, ver- 

 tebrae, and muscles of neighborhood; 



Muscular, to inferior constrictor of pharynx, scalenus antictis, and 

 other muscles. 



4. The suprascapvlar artery (transversalis humeri) pappos 

 beneath the posterior belly of the omo-hyoid to the upper border 

 of the scapula, passing over the transverse ligament of the scapula 

 to the supraspinous fossa, where it is distributed to the supra- 

 spinatus, sterno-mastoid, and other muscles, and by means of the 



