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 | +------------+-----------+---------+---------+ [Illustration: 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.] It is worthy of notice that in birds the number of the cervical vertebræ is not constant, as in mammals; they are more numerous than the dorsal. These latter are almost always joined to one another by a fusion of their spinous processes; the two or three last vertebræ are similarly united to the iliac bones, between which they are fixed. The dorsal vertebræ thus form one piece, which gives solidity to the trunk, and provides a base of support to the wings, for the movements of flying. There are, so to speak, no lumbar vertebræ, the bones of that region, which cannot be differentiated from the sacrum, having coalesced with the bones of the pelvis. VERTEBRÆ.