Skull anatomy other than the ear region of the pen-tailed treeshrew, Ptilocercus lowii Gray, 1848 (Ptilocercidae), is described and illustrated in detail based on 11 specimens from the Carnegie Museum of Natural History and the United States National Museum. Comparisons are made to the common treeshrew, Tupaia glis (Diard, 1820) (Tupaiidae), in a manner similar to the author's treatment of the ear region (Wible 2009). Included are bone by bone treatment of the external surfaces of the skull and hyoid apparatus, and composite treatment of the endocranium for P. lowii with comparisons to an uncertain species of Tupaia Raffles, 1821, and T. glis. The principal cranial foramina and their contents are addressed.
Treeshrews are members of the placental order Scandentia, which is nested within the higher-level clade Euarchonta, along with the order Primates and the order Dermoptera (colugos). Relationships among these three orders are controversial in recent molecular studies, and detailed morphological studies, such as this, provide additional characters for future studies resolving the phylogenetic pattern.