The prefrontal bone is situated, on each side, between the frontal and the maxillary, and may or may not be in contact with the nasal.
The postfrontal, usually present, borders the orbit behind, rarely also above, and in the Pythons a supraorbital is intercalated between it and the prefrontal.
The paired vomer is narrow.
The palatine and pterygoid are elongate and parallel to the axis of the skull, the latter diverging behind and extending to the quadrate or to the articular extremity of the mandible; the pterygoid is connected with the maxillary by the ectopterygoid or transverse bone, which may be very elongate, and the maxillary often emits a process towards the palatine, the latter bone being usually produced inwards and upwards towards the anterior extremity of the basisphenoid.
The quadrate is usually large and elongate, and attached to the cranium through the supratemporal (often regarded as the squamosal).
In rare cases, (Miodon, Polemon) the transverse bone is forked, and articulates with two branches of the maxilla.
The quadrate and the maxillary and palatopterygoid arches are more or less movable to allow for the distension required by the passage of prey, often much exceeding the calibre of the mouth. For the same reason, the rami of the lower jaw, which consist of dentary, splenial, angular, and articular elements, with the addition of a coronoid in the Boidae and a few other small families, are connected at the symphysis by a very extensible elastic ligament.
The hyoid apparatus is reduced to a pair of cartilaginous filaments situated below the trachea, and united in front.
There are various modifications according to the genera. A large vacuity may be present between the frontal bones and the basisphenoid (Psammophis, Coelopeltis); the maxillary may be much abbreviated and movable vertically, as in the Viperidae; the pterygoids may taper and converge posteriorly, without any connexion with the quadrate, as in the Amblycephalidae; the supratemporal may be much reduced, and wedged in between the adjacent bones of the cranium; the quadrate may be short or extremely large; the prefrontals may join in a median suture in front of the frontals; the dentary may be freely movable, and detached from the articular posteriorly.
The deviation from the normal type is much greater still when we consider the degraded wormlike members of the families Typhlopidae and Glauconiidae, in which the skull is very compact and the maxillary much reduced. In the former this bone is loosely attached to the lower aspect of the cranium; in the latter it borders the mouth, and is suturally joined to the premaxillary and the prefrontal. In both the transverse bone and the supratemporal are absent, but the coronoid element is present in the mandible.
The principal modifications of the skull in the European genera may be contrasted as in the following synopsis:
The centra have the usual cup-and-ball articulation, with the nearly hemispherical or transversely elliptic condyle at the back (procoelous vertebrae), whilst the neural arch is provided with additional articular surfaces in the form of pre- and post-zygapophyses, broad, flattened, and overlapping, and of a pair of anterior wedge-shaped processes called zygosphene, fitting into a pair of corresponding concavities, zygantrum, just below the base of the neural spine. Thus the vertebrae of snakes articulate with each other by eight joints in addition to the cup-and-ball on the centrum, and interlock by parts reciprocally receiving and entering one another, like the joints called "tenon-and-mortice" in carpentry. The precaudal vertebrae have a more or less high neural spine which, as a rare exception (Xenopholis), may be expanded and plate-like above, and short or moderately long transverse processes to which the ribs are attached by a single facet. The centra of the anterior vertebrae emit more or less developed descending processes, or haemapophyses, which are sometimes continued throughout (Fig. II, A), as in Tropidonotus, Vipera, and Ancistrodon, among European genera.
In the caudal region, elongate transverse processes take the place of ribs, and the haemapophyses are paired, one on each side of the haemal canal. In the Rattlesnakes the seven or eight last vertebrae are enlarged and fused into one.
A Giant Sauropod Dinosaur from an Upper Cretaceous Mangrove Deposit in Egypt.(African terrestrial vertebrate)(Statistical Data Included)
Jun 01, 2001; In the early 20th century, the Bavarian geologist Ernst Stromer described a diverse biota from the Upper Cretaceous [Cenomanian:...