The =thoracic vertebrae= are twelve or thirteen in number, and all bear movably articulated ribs. As a group they are characterised by their comparative shortness, and in the case of the first eight or nine by the great length of the backwardly-sloping neural spine. The posterior thoracic vertebrae approach in character the succeeding lumbar vertebrae. As type of the anterior thoracic vertebrae, take any one between the second and sixth inclusive. The centrum is short, and has its terminations vertically truncated. At the top of the centrum, at both anterior and posterior ends on each side, is a demi-facet (fig. 70, A, 4), which, together with that on the adjacent vertebra, forms an articulating surface for the capitulum of the rib. The neural arch is small and deeply notched behind for the passage of the spinal nerve. It is drawn out above into a very long neural spine (fig. 70, A, 1), whose base extends back over the succeeding vertebra and bears the downwardly-directed postzygapophyses (fig. 70, A, 6). The summit of the neural arch is deeply notched in front, and on each side of the notch are the prezygapophyses, which look almost vertically upwards. The transverse processes are short and blunt, and are flattened below (fig. 70, A, 3) for the articulation of the tubercula of the ribs. [Illustration FIG. 70. A, SECOND THORACIC, AND B, SECOND LUMBAR VERTEBRA OF A DOG (_Canis familiaris_) SEEN FROM THE RIGHT SIDE (after VON ZITTEL). 1. neural spine. 2. centrum. 3. transverse process bearing in A the facet for articulation with the tuberculum of the rib. 4. facet for articulation with the capitulum of the rib. 5. metapophysis. 6. postzygapophysis.] The posterior three or four thoracic vertebrae differ much from the others. The centra are longer, the neural spines short and not directed backwards, the articular facets for the heads of the ribs are confined to the anterior end of the centrum of each vertebra, not overlapping on to the preceding vertebra. The transverse processes are small and irregular, and metapophyses and anapophyses are developed. The prezygapophyses also look more inwards, and the postzygapophyses more outwards than in the more typical thoracic vertebrae. THE LUMBAR VERTEBRAE. The =lumbar vertebrae= are seven in number, and their general characteristics have been already described. As a group they are characterised by their large size, and the great development of the transverse processes, metapophyses and neural spines. THE SACRAL VERTEBRAE. Three vertebrae are commonly found fused together, forming the =sacrum=; the divisions between the three being indicated by the foramina for the exit of the spinal nerves.