BRANCHES OF THE SUBCL AVIAN ARTERY. 521 



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. 



Bulbar. 



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 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 about the level of the foramen magnum. One of these ves- 

 sels 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 spinal cord, and is rein- 

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

 intervertebral foramina ; these branches are derived from the vertebral and ascend- 

 ing 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, which 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 membrane 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 

 cord and to the cauda equina. Branches from these vessels form a free anasto- 

 mosis round the posterior roots of the spinal nerves, and communicate, by means 

 of very tortuous transverse branches, with the vessel of the opposite side. At its 

 commencement it gives off an ascending branch, which terminates on the side of 

 the fourth ventricle. 



The posterior inferior cerebellar artery (Fig. 291), the largest branch of the 

 vertebral, winds backward round the upper part of the medulla oblongata, passing 

 between the origin of the pneumogastric and spinal accessory nerves, over the 

 restiform body to the under surface of the cerebellum, where it divides into two 



