(Bos taurus) × 1/3. (Camb. Mus.)

1. neural spine.5. facet for articulation with the
2. neural canal.capitulum of the rib.
3. prezygapophysis.6. postzygapophysis.
4. facet for articulation with the7. foramen for exit of spinal
tuberculum of the rib.nerve.

In the Proboscidea there are twenty-three thoraco-lumbar vertebrae, of which nineteen or twenty bear ribs.

In the Rodentia there are generally nineteen thoraco-lumbar vertebrae but occasionally the number rises as high as twenty-five. In the Hares (Leporidae) the number is nineteen, twelve or thirteen of which are thoracic. The anterior thoracic vertebrae have short centra and high backwardly-directed neural spines, the lumbar vertebrae have large forwardly- and downwardly-directed transverse processes with expanded ends. Metapophyses, anapophyses and hypapophyses are all present. In the Agouti (Dasyprocta) the convergence of the neural spines to a centre of motion is very strongly marked.

In the Carnivora the trunk vertebrae are nearly always twenty or twenty-one in number; in the genera Felis and Canis thirteen of these are thoracic and seven lumbar. The anterior thoracic vertebrae have long backwardly-projecting neural spines, while the posterior thoracic and lumbar vertebrae have shorter and thicker neural spines which project slightly forwards. In the Pinnipedia there is no change in the direction of the neural spines, and anapophyses are but little developed.

In the Insectivora the number of trunk vertebrae varies much from nineteen—thirteen thoracic and six lumbar—in Tupaia, to twenty-four—nineteen thoracic and five lumbar—in Centetes. The development of the various processes varies in accordance with the habits of the animals, being great in the active forms, slight in the slowly moving or burrowing forms. In Talpa and Galeopithecus the intervertebral discs of the thoraco-lumbar region instead of being cartilaginous have ossified forming inter centra, a condition met with in very few mammals.

In the Chiroptera there are seventeen or eighteen thoraco-lumbar vertebrae, eleven to fourteen of which may bear ribs. The development of processes is slight.

Among Primates the number of trunk vertebrae is generally nineteen, of which twelve to fourteen bear ribs; in man and the Gorilla and Chimpanzee the number is, however, seventeen, and in the Orang (Simia) sixteen. In some of the Lemuroidea there are as many as twenty-three or twenty-four. In most cases the neural spines converge more or less to a centre of motion, and this is especially marked in some of the Lemurs; it does not occur in man and the anthropoid apes.

Sacral and caudal vertebrae.

At the posterior end of the trunk in all mammals a certain number of vertebrae are found fused together forming the sacrum. But of these only two or three answer to the definition of true sacral vertebrae in being united to the ilia by small ribs. The others which belong to the caudal series may be called pseudosacral vertebrae. In different individuals of the same species it sometimes happens that different vertebrae are attached to the pelvis and form the sacrum. Sometimes even different vertebrae are attached to the pelvis at successive periods in the life history of the individual. This is owing to a shifting of the pelvis and has been especially well seen in man. In young human embryos the pelvis is at a certain stage attached to vertebra 30, but as development goes on it becomes progressively attached to the twenty-ninth, twenty-eighth, twenty-seventh, twenty-sixth and twenty-fifth vertebrae. As the attachment to these anterior vertebrae is gained, the attachment to the posterior ones becomes lost, so that in the adult the pelvis is generally attached to vertebrae 25 and 26. But there are no absolutely pre-determined sacral vertebrae, as sometimes the pelvis does not reach vertebra 25, remaining attached to vertebrae 26 and 27; sometimes it becomes attached even to vertebra 24. This shifting of the pelvis is seen in Choloepus in a more marked degree even than in man.