=Epistropheus= or =Axis= (Fig. 10, 2; Fig. 13).--The second cervical vertebra (epistropheus or axis) is not so wide as the atlas but is much longer. Craniad the centrum is continued into a slender conical, toothlike projection, the =dens= or =odontoid process= (Fig. 13, _a_) which represents the centrum of the atlas. The dens is smooth below for articulation with the ventral arch of the atlas. It is rougher above. Laterad of the dens the centrum bears a pair of large cranial articular facets (_b_) which look craniolaterad. These have each the form of a right-angled triangle with rounded angles, one side of the triangle being nearly horizontal. Each is separated from the articular face of the dens by a roughened groove. The spinous process (_c_) runs the length of the vertebral arch. It extends craniad of the vertebral arch nearly as far as the dens, as a flat rounded projection. Caudad of the vertebral arch it projects for a short distance as a stout triangular spine. The caudal articular facets (_d_) are borne on thickenings of the caudolateral portions of the arch; they face almost directly ventrad. The transverse process (_e_) is slender and triangular and directed nearly caudad. Its apex reaches no farther than the caudal or articular face of the centrum. Its base is traversed by the foramen transversarium (_f_). =Differential Characters of the Cervical Vertebræ.=--It is possible to identify each of the cervical vertebræ: The first by the absence of the centrum. The second by the dens or odontoid process. The third by the small spinous process and slightly marked tubercle of the transverse process, and by a median tubercle on the cranial border of the vertebral arch. The fourth by the spinous process directed dorsad, and the short thick tubercle of the transverse process not trifid. The fifth by the spinous process directed craniad, and the more slender spine-like tubercle of the transverse process not trifid. The sixth by the trifid transverse process. The seventh by the long spinous process and the slender simple transverse process, and by the usual absence of the foramen transversarium. LIGAMENTS OF THE VERTEBRAL COLUMN. =Fibro-cartilagines intervertebrales.=--The separate vertebræ (except the atlas and axis) are united by the disk-shaped =intervertebral fibro-cartilages=, which are situated between the centra of the vertebræ. Each consists of a central pulpy portion and a fibrous outer portion, covered by strong intercrossing tendinous fibers which unite with the periosteum of the vertebræ. =Ligamentum longitudinale anterius.=--On the ventral face of the centra of the vertebræ, from the atlas to the sacrum, lies a longitudinal ligament, the =anterior longitudinal ligament=. It is very small, almost rudimentary, in the cervical region: large and strong in the thoracic and lumbar regions.