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16 (Fig. 33) and Therapsida (Figs. 43, 44, 45), and all other reptiles, they are excluded from the narial margin. They are small or vestigial in the Squamata, and absent in most Chelonia and in Sphenodon (Fig. 60 ). They are of extraordinary size in some Theropoda (Fig. 70 ), articulating posteriorly with the postorbitals. It has been urged by Jaekel and Gaupp that these bones are not the homologues of the mammalian lacrimal, and should be called by another name, for which postnasal and adlacrimal have been proposed.



Prefrontals (pr). Primitively (Figs. 2, 4, 22) at the upper anterior border of the orbits, articulating with lacrimals, nasals, frontals, and postfrontals, and by a descending process with the palatines.

Never absent, though much reduced and excluded from the orbital margin in the Theropoda (Fig. 70 ). Sometimes (Fig. 70 ) they articulate with the postorbitals or postfronto-orbitals when the postfrontals are absent as discrete bones. Below, they articulate with the prevomers in the Chelonia (Fig. 30 ), with the palatines and pterygoids in the Crocodilia (Fig. 69 ). Excluded from the frontals in the