Anatomic description of the Atlas, the Axis and the Prominent vertebra, the first second and cervical vartebra.

The Atlas

The first vertebra, or atlas, (so called from supporting the head,) is an irregular ring of bone, which presents nothing analogous either to the bodies or spines of the other vertebrae. The ring, in the fresh state, is divided into two parts by a transverse ligament, — the anterior one being occupied by the odontoid process of the axis, the posterior by the spinal cord; — it presents in front a small arch of bone, the anterior surface of which is marked by a tubercle posterior by a smooth depression, adapted to the odontoid process of the axis. The posterior segment of the ring is considerably larger than the anterior; at Its middle point it presents a tubercle, which is the analogue of the spinous processes; it is thick and round in the greater part of its extent; but at its junction with the rest of the vertebra there exists on the upper border at each side a smooth groove which lies behind the superior articular process, and marks the tortuous course pursued by the vertebral artery previously to entering the cranium. This groove is analogous to the notches in the other vertebra;, for it transmits the first spinal nerve as well as the vertebral artery ; it is sometimes converted into a foramen by a spiculum of bone. The articulating surfaces are horizontal and large. The superior pairs receive the condyles of the occipital bone; they converge in some sort towards the forepart of the bone; and as their form is oval and their surface concave from before backwards, they look towards one another; at the inner margin of each is a rough surface, which gives attachment to the transverse ligament. The inferior pairs, on the contrary, are flat, and nearly circular in their form. The parts of the vertebra {lateral masses) on which these processes are situated are of very considerable thickness, because the weight of the head, which in others is received by the bodies, rests here on the articular surfaces. The transverse processes project considerably on each side, and terminate in a rounded point; at the root of each is situated the foramen, which transmits the vertebral artery.