_an_, Angular; _ar_, articular; _bo_, basioccipital; _bs_, basisphenoid; _cor_, coronoid; _c.a_, columella auris (stapes); _d_, dentary; _eo_, exoccipital; _epg_, ectopterygoid (transverse); _f_, frontal; _m_, maxillary; _n_, nasal; _p_, parietal; _pl_, palatine; _pm_, premaxillary; _prf_, prefrontal; _pro_, proötic; _pg_, pterygoid; _ptf_, postfrontal; _q_, quadrate; _so_, supraoccipital; _sor_, supraorbital; _sp_, splenial; _ste_, supratemporal; _tu_, turbinal; _v_, vomer.] The premaxillary is single and small, and as a rule connected with the maxillary only by ligament. 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 Boidæ 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 Viperidæ; the pterygoids may taper and converge posteriorly, without any connexion with the quadrate, as in the Amblycephalidæ; 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. [Illustration: FIG. 4--SKULL OF _Typhlops lumbricalis_. (From British Museum Catalogue of Snakes) Lettering of the bones as in Fig. 3] [Illustration: FIG. 5--SKULL OF _Glauconia macrolepis_. (From British Museum Catalogue of Snakes) Lettering of the bones as in Fig. 3]