| OCR Text |
Show 1890.] HELODERMA SUSPECTUM. 217 the sharpened edge of the corresponding coracoid. Such a form as Lacerta viridis, according to Mr. T. J. Parker, has in its sternum characters additional to the ones here described, for it will be observed that Heloderma lacks the "small central fontanelle" and the "two slender flattened cornua" which are produced posteriorly. Indeed, this simple type of sternum in our present subject does not seem to agree exactly with any other form in particular. And to satisfy one's self of this fact it is only necessary to compare the description offered above with the figures of reptilian sterna that have been collected together for us by Hoffmann in Bronn's Thier-Reichs (Rept. 18-21 Lief., 1881). The Skull.-To complete the account of the axial skeleton a consideration of this important part of it still remains. The first thing that strikes one upon a general examination of the skull of Heloderma suspectum is what may be characterized as its peculiar solidity, a certain massive compactness. All the bones composing it are stout and strong. This appearance is still further enbanced by the fact that it is thickly studded for the anterior superficies of its roofing bones by the co-ossified dermal tubercles, and some of these may be found over the parietal region. Old oaken chests or various kinds o! heavy furniture leave the same impressiou upon our minds, when they, too, have certain parts of them studded with round-headed, brass hob-nails. Sutural traces can, but with difficulty, be made out in some instances, although in the mandible and in most other localities no such obliterations are met with. Except in front, the encephalic casket is well protected by bony walls, and this kind of protection is also nearly as well afforded to the orbits and the rhinal spaces; the bounding peripheral margins of these latter are quite circular in outline, while the antero-external narial apertures are very much of the same form. The form of the snout is broadly rounded, and the maxillary alveolar margins are strong and horizontally broad, thus creating a substantial base for the besetment of the teeth. Normally, the massive mandibular rami do not fuse by ossification at the mandibular symphysis. What is one of the most remarkable facts, however, about the skull of this reptile is the now well-known circumstance that its zygomatic arch is almost completely atrophied, and further that by the union of the post- and prefrontal bones, the frontal is most completely prevented from participating in the formation of the orbital periphery. In outline the comparatively large foramen magnum is a transverse ellipse, while the condyle of the occiput below it is reniform in shape and distinctly exhibits throughout life the sutural traces of the bones that enter into its formation. Spacious from side to side, but not lofty, the posterior temporal fossae are much over-arched by the free posterior edge of the parietal bone. Either parotic process is stout, being directed upwards, backwards, and principally outwards, while the various infero-lateral foramina at or near its base are of comparatively large size : relatively larger, for instance, than we find them in the skull of a big Iguana tuberculata that I have at hand. |
