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Description--Skull short (GLS: 18.8 to 20.5 mm); braincase high, dorsal margin slightly flattened; postorbital region very constricted (INC: 7.5 to 7.9 mm); lambdoidal and sagittal crests greatly developed; supraorbital rims elevated, converging posteriorly; coronoid process and mandibular condyle aligned in parallel with the dentary; apical margins of the upper incisors divergent, I2 located diagonally behind I1; upper canines long with a very conspicuous external cingulum; large P4, triangular in occlusal view; p1 smaller than half the size of p2; molar ectolophs W-shaped; M3 broader than long, half the size of M2.
One aging trend in porcupines is the advancement medially of the marginal muscle scars of the temporalis, and the formation of a sagittal crest if the two lateral muscle masses meet along the frontal suture.
The opossum's skull contains a number of strong muscle attachment sites, including a tall, well-defined, bladelike sagittal crest.