Tubules within the cristae of mitochondria can sometimes take on unusual configurations. Here, in the upper panel, a mitochondrion from an astrocyte in hamster brain appears to have prismatic tubules that are triangular in cross section. The lower panel shows a mitochondrion from rat adrenal cortex with what appears to be vesicular cristae. Arrows point to evidence suggesting that instead, these are probalby tubules with alveolar branches. Description here. Figure 245 (upper) by K. Blinzinger, J. Cell Biol. 25: 293, 1965; fig. 246 (lower) courtesy of Daniel Friend, from Chapter 7 (Mitochondria) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. A PDF copy of the accompanying chapter is available on the ASCB's BioEDUCATE website.