| 1. neural spine. | 4. facet for articulation with the |
| 2. centrum. | capitulum of the rib. |
| 3. transverse process bearing in | 5. metapophysis. |
| A the facet for articulation | 6. postzygapophysis. |
| with the tuberculum of the | |
| rib. |
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.
Of these three vertebrae, the first is much the largest, and is firmly united to the ilium on each side by a structure formed by the transverse processes and expanded ribs. In the adult this structure forms one continuous mass, but in the young animal a ventral portion formed by the rib is clearly distinguishable from a dorsal portion formed by the transverse process. All three have low neural spines. The anterior sacral vertebra bears a large pair of prezygapophyses, while the posterior one bears a small pair of postzygapophyses.
The Caudal vertebrae.
The caudal vertebrae are about nineteen in number. The earlier ones have well-developed neural arches, transverse processes, and zygapophyses, but as the vertebrae are followed back they gradually lose all their processes, and the neural arch as well, becoming at about the thirteenth from the end reduced to simple cylindrical centra.
B. The Skull.