This only means that the equipotential surfaces are crowded together, just as they are near the ridge of a house.
In the late seventies and early eighties scaling these challenging surfaces really caught on.
The plates are compressed from before backwards, the anterior and posterior surfaces (as seen in the worn grinding face of the tooth) being nearly parallel.
The molar teeth are of coarse construction, with fewer and larger plates and thicker enamel; the ridge-formula being 3, 6, 7, 8, io; while the plates are not flattened, but thicker in the middle than at the edges, so that their worn grinding-surfaces are lozengeshaped.
The second book is in nine propositions, eight of which deal with segments of spheres and include the problems of cutting a given sphere by a plane so that (a) the surfaces, (b) the volumes, of the segments are in a given ratio (Props.