Often a ridge has low areas along it, not necessarily separating the ridge into two parts, but enough so that one or several contours close, or at least pinch closer together. When you scan the z values in this map, look for a trend of a ridge from lower left toward upper right (higher z values, in the 600-700 range). But, notice how the z values drop along this ridge toward the center, where there are several points with z values in the 600 range:
Contours of this data show the contours of 650, 700, and 750 to stay on either end of the ridge, so that there is a saddle in the middle of the map, which is just a low area along the ridge:
Why is a saddle called a saddle? Well, have you looked at a horse's back lately? The saddle rests in a kind of smooth downward "swoop" of the horse's back.
Horse parts, from Wikipedia
And, if you are really interested in horse parts, the saddle fits between the withers and the croup (rump). Note, if you scan the horse part names, that the knee of the horse is the same as your wrist -- a potential confusion!