BASE, AND ITS MODIFICATIONS. 149 



Modifications. 



Class a. Terminal solid angles replaced by tangent 

 planes. 



Class b. Terminal solid angles replaced by two 

 planes, resting on the obtuse edges of the pyramids. 



Class c. Terminal solid angles replaced by two 

 planes, resting on the acute edges of the pyramids. 



Class d. Terminal solid angles replaced by four 

 planes, resting on the primary planes. 



The edges of the planes c?, which intersect the 

 primary planes, are parallel to the edges of the base. 



