The first or =atlas= vertebra differs much from any of the others, and consists of four quite detached portions, a ventral arch, with two lateral portions and one dorsal. The =ventral arch= (fig. 41, 4) is flat below and slightly concave in front, forming together with two flattened surfaces on the lateral portions a large articulating surface for the occipital condyle of the skull. Its posterior face is bevelled off and forms with a second pair of facets on the lateral portions a surface with which the odontoid process of the second vertebra articulates. The postero-lateral surfaces of the ventral arch also bear a pair of little facets with which the cervical ribs articulate. The lateral portions are somewhat flattened and expanded, and bear in addition to those previously mentioned a pair of small downwardly directed facets, the postzygapophyses, which articulate with the prezygapophyses of the second vertebra. The dorsal portion (fig. 41, 1) is somewhat triangular in shape, and overhangs the occipital condyle. It is often regarded as the neural arch of a vertebra in front of the atlas and is called the _pro-atlas_; but as it is a membrane bone it is not properly a vertebral element.
The second or =axis vertebra= also differs a good deal from the other cervicals. The centrum is massive, and is terminated in front by a very large slightly concave articulating surface formed by the =odontoid process= (fig. 41, 3) which is united with the centrum by suture only, and is really the detached centrum of the first vertebra. The cervical rib (fig. 41, 9) articulates with two little irregularities on the odontoid process. The posterior surface of the centrum is convex. The neural arch is strongly developed and terminated dorsally by a long neural spine (fig. 41, 5), its sides are notched, slightly in front and more prominently behind for the exit of the spinal nerves. It is drawn out in front into two little processes bearing a pair of upwardly and outwardly directed prezygapophyses, while the postzygapophyses are similar to those of the other cervical vertebrae.
The last two cervical vertebrae resemble the succeeding thoracic vertebrae, in the increased length of the transverse processes, and the shifting dorsalwards of the facet with which the capitulum of the rib articulates.