. Cope papers, 1871-[1897. Zoology; Paleontology. 198 B. KATUEAL HISTOEY. mosal, not only on this account, but because, as in other Reptilia, it is articulated with the summit of the quadrate. Turning again to the posterior face of the cranium, we may be in a position to determine the two bones described above as lying outside of the occipitals, and between them and the quadrate and the squamosals. The superior (Op. O, fig. 2) occupies the position of the " external occipital" of Cuvier, in the tortoise, both by its articulation with the exoccipital (Ex. O) and its direction towards
. Cope papers, 1871-[1897. Zoology; Paleontology. 198 B. KATUEAL HISTOEY. mosal, not only on this account, but because, as in other Reptilia, it is articulated with the summit of the quadrate. Turning again to the posterior face of the cranium, we may be in a position to determine the two bones described above as lying outside of the occipitals, and between them and the quadrate and the squamosals. The superior (Op. O, fig. 2) occupies the position of the " external occipital" of Cuvier, in the tortoise, both by its articulation with the exoccipital (Ex. O) and its direction towards the squamosal (Sq). Its separation from the supraoccipital, and contact with the basioccipital, are against this determination, yet Fig. 1.* (5 A<ww op I -Art. the weight of these arguments is much less than that of those for it; and therefore I suppose it to represent that bone, which is the opisthotic of modem nomenclature. The large foramen below the last, and exterior to the basi- occipital, is in the position of the opening of the internal ear in the Lacertilia, as regards its relation to the latter bone, the opis- thotic being separated from it by the extension outwards of the exoccipital. Its relation to the opisthotic is the same as that in the Cheloniidse, where it is separated from the basioccipital by an in- ferior process of the exoccipital. It is probably the fenestra ovale; and, if so, the second bone in question (stap) becomes the stapes. It is a question, however, to what extent this element is really *. Fig. 1.—Ichthyosaurus; lateral view (from specimen from Barrow, Leices- tershire). Pmi. Premaxillary hone. Mx. . Maxillary. N Nasal. Fr Frontal. Prf. . Prefrontal. Pof. . Postfrontal. Pa. . Parietal. L. . Lachrymal. . Malar. Qj. . - Quadratojugal. Q Quadrate. Pob. . Postorbital. Sq. . Squamosal. . ..Dentary. An. . Angular. At. . Articular. S. Ar. Subarticular. Pter. . Please note that these images are extracted from scanned page images t
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