Vertebral artery in the context of Subclavian arteries

In tetrapods, cervical vertebrae (sg.: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In sauropsid species, the cervical vertebrae bear cervical ribs. In lizards and saurischian dinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. The vertebral transverse processes of mammals are homologous to the cervical ribs of other amniotes. Most mammals have seven cervical vertebrae, with the only three known exceptions being the manatee with six, the two-toed sloth with five or six, and the three-toed sloth with nine.

In humans, cervical vertebrae are the smallest of the true vertebrae and can be readily distinguished from those of the thoracic or lumbar regions by the presence of a transverse foramen, an opening in each transverse process, through which the vertebral artery, vertebral veins, and inferior cervical ganglion pass. The remainder of this article focuses on human anatomy.

The foramen magnum is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblongata, passes through the foramen magnum as it exits the cranial cavity. Apart from the transmission of the medulla oblongata and its membranes, the foramen magnum transmits the vertebral arteries, the anterior and posterior spinal arteries, the tectorial membranes and alar ligaments. It also transmits the accessory nerve into the skull.

Bipedal species typically display an anteriorly placed foramen magnum to balance the head atop the vertebral column. In hominins, this anterior shift is uniquely coupled with increased cranial base flexion. Studies of foramen magnum position have shown its relationship to posture and locomotion. This forward placement is apparent in bipedal hominins such as modern humans, Australopithecus africanus, and Paranthropus boisei. This common feature of bipedal hominins is the driving argument used by the paleontologist Michel Brunet to support that Sahelanthropus tchadensis was bipedal and may be the earliest known bipedal hominin. The recognition of this feature has given scientists another tool for identifying bipedal mammals.

The vertebral vein is formed in the suboccipital triangle, from numerous small tributaries which spring from the internal vertebral venous plexuses and issue from the vertebral canal above the posterior arch of the atlas.

They unite with small veins from the deep muscles at the upper part of the back of the neck, and form a vessel which enters the foramen in the transverse process of the atlas, and descends, forming a dense plexus around the vertebral artery, in the canal formed by the transverse foramina of the upper six cervical vertebrae.

In human anatomy, the anterior spinal artery is the artery that supplies the anterior portion of the spinal cord. It arises from branches of the vertebral arteries and courses along the anterior aspect of the spinal cord. It is reinforced by several contributory arteries, especially the artery of Adamkiewicz.

The posterior spinal artery (dorsal spinal arteries) arises from the vertebral artery in 25% of humans or the posterior inferior cerebellar artery in 75% of humans, adjacent to the medulla oblongata. It is usually double, and spans the length of the spinal cord. It supplies the grey and white posterior columns of the spinal cord.

In human anatomy, the subclavian arteries are paired major arteries of the upper thorax, below the clavicle. They receive blood from the aortic arch. The left subclavian artery supplies blood to the left arm and the right subclavian artery supplies blood to the right arm, with some branches supplying the head and thorax. On the left side of the body, the subclavian comes directly off the aortic arch, while on the right side it arises from the relatively short brachiocephalic artery when it bifurcates into the subclavian and the right common carotid artery.

The usual branches of the subclavian on both sides of the body are the vertebral artery, the internal thoracic artery, the thyrocervical trunk, the costocervical trunk and the dorsal scapular artery, which may branch off the transverse cervical artery, which is a branch of the thyrocervical trunk. The subclavian becomes the axillary artery at the lateral border of the first rib.