The sagittal depth , " s " , ( also called sagitta , sagittal height or sag ) is the perpendicular distance between the geometric center of the back lens surface and the diameter of the lens .
矢深,“s”,(又称矢高、弧高或垂距),指镜片内曲面的几何学中心至线状直径之间的垂直距离。
Among them , meriones meridianus was the first dominant species , rhombomys opimus the second dominant species , dipus sagitta the common species , and rare species were allactaga elater , m. tamariscinus and mus musculus .