Several cranial structures are described for the first time in the Lower Permian seymouriamorph tetrapod Seymouria sanjuanensis: 1) septomaxilla, 2) suborbital fenestra, 3) small denticles on the palate densely spaced in compact rows radiating from a point near the midwidth of the posterior margin of the palatal ramus of the pterygoid, 4) long cultriform process, and 5) posterior Meckelian fenestra. The possible presence of the paraquadrate foramen is also described. In addition, a more detailed description is given for the relationships between the maxilla, jugal, and quadratojugal on the ventral rim of the skull and between the nasolacrimal canal and the anteroventral orbital notch. Reconstructions of the skull include revised dorsal and lateral views and a first time ventral view.