. Cope papers, 1871-[1897. Zoology; Paleontology. 222 B. NATTJEAL HISTOET. arch, as in Ichthyosaurus and Lystrosaurus, diifering only in its elevation above the occipital elements as an arch, instead of being closely depressed upon them. It has been already suggested in this essay, that this portion may include the epiotic element. The second peculiarity is observed in Sphenodon, and is quite unparalleled. This is that the opisthotic expands over the exter- nal face of the squamosal, concealing it from outside view, and occupies the greater part of the posterior face of the parieto-quad- rate
. Cope papers, 1871-[1897. Zoology; Paleontology. 222 B. NATTJEAL HISTOET. arch, as in Ichthyosaurus and Lystrosaurus, diifering only in its elevation above the occipital elements as an arch, instead of being closely depressed upon them. It has been already suggested in this essay, that this portion may include the epiotic element. The second peculiarity is observed in Sphenodon, and is quite unparalleled. This is that the opisthotic expands over the exter- nal face of the squamosal, concealing it from outside view, and occupies the greater part of the posterior face of the parieto-quad- rate arch. Its position suggests at first the inquiry whether the identification of the two elements here adopted is not the reverse of the true one. The relations of the opisthotic to the exoccipital are, however, as elsewhere; while the squamosal forms the inner side of the zygomatic arch behind, and occupies in part the posi- tion seen in Lystrosaurus. The third peculiarity already described is the posterior inferior production of the squamosal in Ichthyosaurus and Lystrosaurus. In the latter it is very remarkable, and covers the outer side of the quadrate completely. The last feature is alluded to for the purpose of caiTying the homology of the squamosal into the Batrachia. Huxley (Elements Compara- tive Anatomy) does not allow himself to compare any element in that class with this bone in the Reptilia, and, alluding to the " tympanique " (Cu- Fig. 21. — Cranium of Eana mugiens; profile. vier) of the frog, says it is too difierent from the squamosal to be compared with it. If, however, he had had the cranial structure of Lystrosaurus, he could no longer have doubted, but would have homologized them at once. (Figs. 21, 23, Sq.) Dr. W. K. Parker has ventured on this step, and identified the squa- mosal in the Batrachia, in accordance with the n&. FT ExO. Please note that these images are extracted from scanned page images that may have been digitally enhanced for r
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