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Show 218 DR. R. W. SHUFELDT ON [Apt. 1, The posterior nasal fossa, are elongo-pear-shaped apertures with the bulbous ends directed backwards, while either palatine foramen is of an oval outline and of no great size. The inferior temporal fossa is capacious, and a firm thin plate of cartilage standing vertically in the median plane divides the orbital cavities internally. This is the interorbital septum. Of fair extent, the basis cranii is nearly a horizontal surface, showing but a very slight general concavity over it. This is at variance with such a form as Iguana tuberculata, where the area to which we refer is considerably concaved. In a previous paragraph we have already sufficiently referred to the tympano-eustachian fossa and the characters of the columella auris. Whatever may be the condition of the parietal ossifications in the very young Heloderma, they are in the adult reptile represented solely by a solidly ossified and dense plate of bone. This bifurcates behind, and either limb is directed backwards and outwards and slightly downwards to articulate with the squamosal of the same side as well as with the corresponding parotic process. Viewed from above the anterior margin of the parietal plate is represented by a finelv serrated transverse line; the superior surface of the bone is nearly horizontal and usually supports a group of the ossified dermal tubercles, which have fused with it. Near the middle of its ventral surface is seen a small pit, which it would seem is situated too far back to represent the vestige of the parietal foramen. It by no means pierces the bone. At some distance within its external free margin, on either side, this bone develops a longitudinal ridge. This is most conspicuous near its middle, and resting here against its outer aspect are the upper ends of the columella and the prootic. In old specimens of this Reptile, the frontal hones areindistinguish-ably fused together, and upon a superior aspect of the skull not a trace of the median suture that originally stood between them can be made out. And even within the cranium it is hardly to be discerned at all. By a straight transverse coronal suture, this frontal bone articulates posteriorly with the parietal; while we have already mentioned the fact as to how it is prevented from participating in the formation of the orbital periphery by the meeting of the pre-and postfrontal elements. Posteriorly, these united frontals are almost entirely masked from our view by the layer of fused and ossified dermal tubercles that overlie the entire fore part of the skull. One never meets with skulls of old individuals of H. suspectum as free from this feature, nor with the naso-frontal and fronto-parietal sutures anything like as clearly defined as is seen in the skull of H. horridum which is figured for us by Mivart (Encycl. Brit. 9th ed. vol. xx. p. 451, fig. 12 / . ) . Ventrally, the frontals of the skull of our present subject offer us a peculiar character. Opposite the orbits each one sends downwards and inwards a broad and curved plate of bone which mesially meets and fuses with a corresponding plate coming from the bone of the other side. This arrangement gives rise to a transverse osseous bridge, and the large mesial foramen it assists to form has passing through it certain |