The Vertebral Column
We commence the study of the skeleton with a description of the trunk.
Fig. 1.—A Human Skeleton in the Attitude of a Quadruped. To give a general Idea of the position of the Bones in other Vertebrates.
The trunk being, in quadrupeds, horizontal in direction ([Fig. 1]), the two regions of which it consists occupy, for this reason, the following positions: the thorax occupies the anterior part, the abdomen is placed behind it; the vertebral column is horizontal, and is situated at the superior aspect of the trunk; it projects beyond the latter: anteriorly, to articulate with the skull; and, posteriorly, to form the skeleton of the tail, or caudal appendix.
The number of the vertebræ is not the same in all mammalia. Of the several regions of the vertebral column, the cervical shows the greatest uniformity in the number of the vertebræ of which it consists, with but two exceptions (eight or nine in the three-toed sloth, and six in the manatee); we always find seven cervical vertebræ, whatever the length of the neck of the animal. There are no more than seven vertebræ in the long neck of the giraffe, but they are very long ones; and not less than seven in the very short neck of the dolphin, in which they are reduced to mere plates of bone not thicker than sheets of cardboard. If the cervical region presents uniformity in the number of its bones, it is not so with the other regions of the column.
The following table shows their classification in some animals:
Vertebræ.
| Cervical. | Dorsal. | Lumbar. | |
| Bear | 7 | 14 | 6 |
| Dog | 7 | 13 | 7 |
| Cat | 7 | 13 | 7 |
| Rabbit | 7 | 12 | 7 |
| Pig | 7 | 14 | 6 or 7 |
| Horse | 7 | 18 | 6 or 5 |
| Ass | 7 | 18 | 5 |
| Camel | 7 | 12 | 7 |
| Giraffe | 7 | 14 | 5 |
| Ox | 7 | 13 | 6 |
| Sheep | 7 | 13 | 6 |