Just like there are certain figures that can be used to tessellate a Euclidean plane, there are certain figures that can tessellate a sphere. In the figure below, the sphere is tessellated with 8 trirectangular spherical triangles ([url]http://books.google.com/books?id=OwmF0wxXfIUC&pg=PA460&lpg=PA460&dq=robbin%27s+plane+and+solid+geometry+trirectangular&source=bl&ots=qwMZkfgS-1&sig=PyFrEde55MeFpEsUMLcx7uhMtBc&hl=en&sa=X&ei=YbW0U-TNOaG_8QHF-oHIBw&ved=0CB0Q6AEwAA#v=onepage&q=robbin's%20plane%20and%20solid%20geometry%20trirectangular&f=false[/url]
