VERTEBRAL. 473 



is given off from the upper and back part of the second portion of the artery. 

 On the left side, the second portion usually gives off no branch, the superior 

 intercostal 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 existing 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 exists, never exceeding an inch and three-quarters. In a very few in- 

 stances, the interval has been found less than half an inch. 



The- Vertebral Artery (Fig. 279) 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 trans- 

 verse processes of all the vertebras above this. Above the upper border of 

 the axis, it inclines outwards 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 Yarolii, 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 accom- 

 panied by a plexus of nerves from the sympathetic, and lies between the ver- 

 tebral vein, which is in front, and the cervical nerves, which issue from the 

 inter vertebral foramina behind it. Whilst winding round the articular process 

 of the atlas, it is contained in a triangular space formed by the Eectus Posticus 

 Major, the Superior and the Inferior Oblique muscles ; and is covered by the 

 Rectus Posticus Major and Complexus. Within the skull, as it winds round 

 the medulla oblongata, it is placed between the bypoglossal nerve and the an- 

 terior root of the suboccipital nerve. 



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

 and those within the cra'nium. 



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 vertebras. 



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 anas- 

 tomose with the occipital 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, 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 sue- 



