396 /ARTERIES. 



costal arising at the inner side of the Scalenus anticus. On "both sides of the body, 

 the first three branches arise close together at the inner margin of the Scalenus 

 anticus ; in the majority of cases, a free interval of half an inch to an inch exist- 

 ing between the commencement of the artery and the origin of the nearest branch ; 

 in a smaller number of cases, an interval of more than an inch existed, never 

 exceeding an inch and three-quarters. In a very few instances, the interval was 

 less than half an inch. 



The VEETEBEAL AETEEY (fig. 212) is generally the first and largest branch of 

 the subclavian ; it arises from the upper and back part of the first portion of the 

 vessel, and, passing upwards, enters the foramen in the transverse process of the 

 sixth cervical vertebra, and ascends through the foramina in the transverse processes 

 of all the vertebras above this. Above the upper border of the axis, it inclines out- 

 wards and upwards to the foramen in the transverse process of the atlas, through 

 which it passes ; it then winds backwards behind its articular process, runs in a 

 deep groove on the surface of the posterior arch of this bone, and, piercing the 

 posterior occipito-atloid ligament and dura mater, enters the skull through the 

 foramen magnum. It then passes in front of the medulla oblongata, and unites 

 with the vessel of the opposite side at the lower border of the pons Varolii, to 

 form the basilar artery. 



At its origin, it is situated behind the internal jugular vein, and inferior thyroid 

 artery ; and, near the spine, lies between the Longus colli and Scalenus anticus 

 muscles, having the thoracic duct in front of it on the left side. Within the foramina 

 formed by the transverse processes of the vertebras, it is accompanied by a plexus 

 of nerves from the sympathetic, and lies between the vertebral vein, which is in 

 front, and the cervical nerves, which issue from the intervertebral foramina behind 

 it. Whilst winding round the articular process of the atlas, it is contained in a 

 triangular space formed by the Rectus posticus minor, the Superior and Inferior 

 oblique muscles ; and it is covered by the Rectus posticus major and Complexus. 

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

 the hypoglossal and anterior root of the suboccipital nerves. 



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. 



Inferior cerebellar. 



The lateral spinal branches enter the spinal canal through the intervertebral 

 foramina, each dividing 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 spinal arteries ; the other is distributed to 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 deep cervical arteries. 



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

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

 mater in the cerebellar fossa?, and supply the falx cerebelli. 



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

 arises near the termination of the vertebral, and unites with its fellow of the 

 opposite side in front of the medulla oblongata. The single trunk thus formed 

 descends a short distance on the front of the spinal cord, and joins with a 

 succession of small branches which enter the spinal canal through some of the 

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

 ing cervical, in the neck ; fronTthe intercostal, in the dorsal region ; and from the 



