

THE SUBCLAVIAN ARTERY 579 



bounded by the Rectus capitis posterior major, the Obliquus superior, and the Obliquus inferior. 

 The first cervical or suboccipital nerve lies between the artery and the posterior arch of the atlas. 

 The fourth part pierces the dura mater and inclines medialward to the front of the medulla 

 oblongata; it is placed between the hypoglossal nerve and the anterior root of the first cervical 

 nerve and beneath the first digitation of the ligamentum denticulatum. At the lower border 

 of the pons it unites with the vessel of the opposite side to form the basilar artery. 



Branches. The branches of the vertebral artery may be divided into two sets: 

 those given off in the neck, and those within the cranium. 



Cervical Branches. Cranial Branches. 



Spinal. Meningeal. 



Muscular. Posterior Spinal. 



Anterior Spinal. 



Posterior Inferior Cerebellar. 



Medullary. 



Spinal Branches (rami spinales) enter the vertebral canal through the interverte- 

 bral foramina, and each divides into two branches. Of these, one passes along 

 the roots of the nerves to supply the medulla spinalis and its membranes, anasto- 

 mosing with the other arteries of the medulla spinalis; the other divides into an 

 ascending and a descending branch, which unite with similar branches from the 

 arteries above and below, so that two lateral anastomotic chains are formed on the 

 posterior surfaces of the bodies of the vertebrae, near the attachment of the pedicles. 

 From these anastomotic chains branches are supplied to the periosteum and the 

 bodies of the vertebrae, and others form communications with similar branches from 

 the opposite side; from these communications small twigs arise which join similar 

 branches above and below, to form a central anastomotic chain on the posterior 

 surface of the bodies of the vertebrae. 



Muscular Branches are given off to the deep muscles of the neck, where the 

 vertebral artery curves around the articular process of the atlas. They anastomose 

 with the occipital, and with the ascending and deep cervical arteries. 



The Meningeal Branch (ramus meningeus; posterior meningeal branch] springs 

 from the vertebral opposite the foramen magnum, ramifies between the bone 

 and dura mater in the cerebellar fossa, and supplies the falx cerebelli. It is fre- 

 quently represented by one or two small branches. 



The Posterior Spinal Artery (a. spinalis posterior; dorsal spinal artery) arises 

 from the vertebral, at the side of the medulla oblongata; passing backward, it 

 descends on this structure, lying in front of the posterior roots of the spinal nerves, 

 and is reinforced by a succession of small branches, which enter the vertebral 

 canal through the intervertebral foramina; by means of these it is continued to 

 the lower part of the medulla spinalis, and to the cauda equina. Branches from 

 the posterior spinal arteries form a free anastomosis around the posterior roots 

 of the spinal nerves, and communicate, by means of very tortuous transverse 

 branches, with the vessels of the opposite side. Close to its origin each gives off 

 an ascending branch, which ends at the side of the fourth ventricle. 



The Anterior Spinal Artery (a. spinalis anterior; ventral spinal artery) is a small 

 branch, which arises near the termination of the vertebral, and, descending in 

 front of the medulla oblongata, unites with its fellow of the opposite side at the 

 level of the foramen magnum. One of these vessels is usually larger than the other, 

 but occasionally they are about equal in size. The single trunk, thus formed, 

 descends on the front of the medulla spinalis, and is reinforced by a succession 

 of small branches which enter the vertebral canal through the intervertebral 

 foramina ; these branches are derived from the vertebral and the ascending cervical 

 of the inferior thyroid in the neck; from the intercostals in the thorax; and from 

 the lumbar, iliolumbar, and lateral sacral arteries in the abdomen and pelvis. 

 They unite, by means of ascending and descending branches, to form a single 



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