Seismometers are instruments that measure motions of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources. Records of seismic waves allow seismologists to map the interior of the Earth, and locate and measure the size of these different sources.
Normally, there are 18 pairs of ribs in the horse, but a nineteenth rib on one side or both is not considered all that rare. Eight pairs of ribs are known as true ribs. They join the segments of the sternum or breastbone. The other 10 are known as floating ribs–merely overlapping and being attached to each other.