Umbilici meaning : Navel Hilum A depression or opening in the center of the base of many spiral shells. Either of the two apertures in the calamus of a feather. A tube connecting an astronaut or spacecraft to the mothership, through which supplies and samples can be transferred. One of the foci of an ellipse or other curve. A point of a surface at which the curvatures of the normal sections are all equal to each other. An ornamented or painted ball or boss fastened at each end of the stick on which manuscripts were rolled.