582 THE ARTERIES. 



vertebral vein at the lower part of the neck. It is situated in front of the cervical 

 nerves as they issue from the intervertebral foramina. Whilst winding round the 

 articular process of the atlas it is contained in a triangular space (suboccipital 

 triangle) formed by the Rectus capitis posticus major, the Superior and the Inferior 

 oblique muscles ; and at this point is covered by the Complexus muscle. Within 

 the skull, as it winds round the medulla oblongata, it is placed between the hypo- 

 glossal nerve and the anterior root of the suboccipital nerve, beneath the first 

 digitation of the ligamentum denticulatum, and finally lies between the dura mater 

 covering the basilar process of the occipital bone and the anterior surface of the 

 medulla oblongata. 



Branches. These may be divided into two sets those given off in the neck 

 and those within the cranium. 



Cervical Branches. Cranial Branches. 



Lateral Spinal. Posterior Meningeal. 



Muscular. Anterior Spinal. 



Posterior Spinal. 



Posterior Inferior Cerebellar. 



The lateral spinal branches enter the spinal canal through the intervertebral 

 foramina and divide into two branches. Of these, one passes along the roots of 

 the nerves to supply the spinal cord and its membranes, anastomosing with the 

 other arteries of the spinal cord ; the other divides into an ascending and a 

 descending branch, which unite with similar branches from the artery above and 

 below, so that two lateral anastomotic chains are formed on the posterior surface 

 of the bodies of the vertebrae near the attachment of the pedicles. From these 

 anastomotic chains branches are given off to supply the periosteum and the bodies 

 of the vertebrae, and to communicate with similar branches from the opposite side ; 

 from these latter small branches are given off which join similar branches above 

 and below, so that a central anastomotic chain is formed 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 round the articular process of the atlas. They anastomose 

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



The posterior meningeal are one or two small branches given off from the 

 vertebral opposite the foramen magnum. They ramify between the bone and dura 

 mater in the cerebellar fossae, and supply the falx cerebelli. 



The anterior spinal is a small branch, though larger than the posterior spinal, 

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

 medulla oblongata, unites Avith its fellow of the opposite side at about the level of 

 the foramen magnum. The single trunk, thus formed, descends on the front 

 of the spinal cord, and is reinforced by a succession of small branches which 

 enter the spinal canal through the intervertebral foramina ; these branches are 

 derived from the vertebral and ascending cervical of the inferior thyroid in the 

 neck ; from the intercostal in the dorsal region ; and from the lumbar, ilio- 

 lumbar, and lateral sacral arteries in the lower part of the spine. They unite, by 

 means of ascending and descending branches, to form a single anterior median 

 artery, Avhich extends as far as the lower part of the spinal cord. This vessel is 

 placed in the pia mater along the anterior median fissure : it supplies that mem- 

 brane and the substance of the cord, and sends off branches at its lower part to 

 be distributed to the cauda equina, and ends on the central fibrous prolongation 

 of the cord. 



The posterior spinal arises from the vertebral at the side of the medulla 

 oblongata : passing backward to the posterior aspect of the spinal cord, it descends 

 on each side, lying behind the posterior roots of the spinal nerves, and is 

 reinforced by a succession of small branches which enter the spinal canal through 

 the intervertebral foramina, and by which it is continued to the lower part of the 



