There are 5 thoracic vertebrae, but the last one is fused into the synsacrum, and the first four are fused together. The last thoracic, all the lumbar, the 2 sacral and several caudal vertebra all fuse to form one bone, the Synsacrum. This in turn is fused to the pelvic girdle. There are several free caudal vertebrae which end in an enlarged Pygostyle, which represents several fused vertebrae. The ribs bear posteriorly projecting Uncinate processes, each being ankylosed to the next posterior rib, the distal region of the ribs are joined to the sternum via sternal processes.
Mammals Note the five vertebral regions - cervical, thoracic, lumbar, sacral and caudal.
Only the thoracic vertebrae bear ribs. The ribs are double headed. The three sacral vertebrae fuse to form one bone, the sacrum, with which the pelvic girdle articulates. Examine the vertebrae on demonstration and in the cat skeleton. Note the differences between vertebrae from different body regions.