Page:EB1911 - Volume 23.djvu/168

ANATOMY] upper anterior end of the quadrate; between the quadrate, the squamosal and the long parietal process lies the likewise splint-like supratemporal, attached by most of its length to the parietal process. The jugal has only one arm, and this connects the maxilla with the postorbital, completing the posterior orbital border. There is a wide gap between jugal and quadrate. In Tejidae the arcade is the same, but the squamosal reaches the jugal, both meeting the post orbital. In Lacerta the arcade is essentially the same, but the window is completely filled up by the post frontal, which extends so far back as to reach the 20.—Dorsal aspect of skull of Heloderma horridum. f, frontal; j, jugal; l, lachrymal; m, maxilla; n, nasal; pa, parietal, pm, premaxilla; pr, prefrontal; ps, postfrontal; pt, pterygoid; q, quadrate; s, squamosal; so, supraoccipital. supratemporal. In the Agamidae the arcade is strong and simplified. Postfrontal and postorbital are represented by one forked piece. This squamosal and the postfrontal mass are connected by the upper, much up-curved end of the jugal, which is thrust between them. This arrangement is further emphasized in Iguana, the upper end of the jugal being much enlarged so as to form the greater portion of the arcade, and keeping the post frontal mass and the simple squamosal widely asunder. In Heloderma post- and prefrontals are in contact with each other, separating the frontal bone from the orbit; the jugal joins only the prefrontal, and there is no further arcade whatever. A vestige of a supratemporal (?) lies on the outside of the base of the squamosal, between s and q in fig. 20.

The chameleons are peculiar. The posttemporal arcade, spanning a wide space, is formed by a long process of the 21.—Skull of Chamaeleon vulgaris. ag, angular; ar, articular; bs, basisphenoid; d, dentary; j, jugal; m, maxilla; me, median ethmoid; p¹ and p², parietals; pl, palatine; pr, prefrontal; pt, pterygoid; q, quadrate; sg, supra-angular; so, supraoccipital; sq, squamosal. supratemporal-squamosal, which is directed up- and backwards to join the parietal, which extends back by a long unpaired process. The horizontal arch is broad and short, squamosal and postfrontal, forming a broad suture; below they are joined by the jugal; above the suture lies, in chameleon, a tiny piece, perhaps a vestige of the dislodged postorbital.

The jugal bones, to continue the description, of the appendicular parts of the skull, are firmly joined to lateral processes of the pterygoids by the ectopterygoids; further forwards they are extensively connected with the maxillaries. These rest against strong transverse palatine processes. The palatines form a medium symphysis; posteriorly they diverge together with the pterygoids, which articulate with the quadrates and with the basisphenoid by a pair of strong basipterygoid processes. A slender vertical rod of bone, the columella cranii, arises from the dorsal surface of each pterygoid and, passing at a distance from the cranial capsule, is sutured to a short lateroventral process of the parietals. Such a pair of columellæ exists in nearly all Lacertilia (distinguished by many systematists as Kionocrania) with the exception of the chameleons and the Amphisbaenidae. In many lizards, however, this columella, or epipterygoid, does not quite reach the parietal, leaning instead against the proötic; possibly it has been evolved out of the alisphenoid, and Chelonians seem to support this view. The premaxillary bone is single, except in the Skinks and in some Geckos; ventrally it touches the vomers which vary much in size; they are always paired although suturally connected; posteriorly they pass into, and fuse with, the palatines before these send off their maxillary processes. Between the vomer and its maxillary is a longitudinal hole. Often, e.g. in Lacerta, the vomers enclose a median hole near their anterior end, for Jacobson’s organ. Dorsally the premaxilla sends a median process backwards to the nasals. These are paired, and fuse together only in Uroplates and in Varanus. The external nasal fossae are sometimes very large, and their anterior half appears blocked by the ossified turbinals, e.g. in Varanus and Tejus. Prefrontals are always present, often fused with the lacrymals; in Heloderma, in Aniella and in chameleons the prefrontals extend so far back as to meet the postfrontals, excluding thereby the frontals from the orbital rim. The frontals are either paired, as in Varanus, Lacertidae, Heloderma, Anguidae, Scincidae, Anelytropsidae, Aniella, Amphisbaenidae, and in some Geckoninae; or they are fused into one bone, as in the Eublepharinae, chameleons, Tejidae, Iguanidae, Agamidae, Xenosaurus. The parietal are double in the Geckos, in Uroplates and Xantusia; in all the others they form one coössified mass, generally with a pineal foramen, except in Eublepharinae, Amphisbaenidae, Tejidae, in Aniella and other degraded forms. In the majority the pineal foramen lies in the middle of the parietal, but in the Iguanidae it is near the frontal, and actually in the frontal in chameleons.

As regards the brain-case, there is a cartilaginous interorbital septum, connected posteriorly with the slender, bony presphenoid; ventrally on to this is fused a vestige of the parasphenoid, a narrow and thin splint which sometimes can be dislodged. The whole of the anterior wall of the brain-case is membranous, excepting a pair of separate ossifications, which do but rarely touch any of the cranial bones, as frontal, parietal or proötics. The ossifications are irregular in shape, each sending out a downward process which curves inwards almost to meet its fellow; between these issue the olfactory lobes. W. K. Parker recognized them as the alisphenoids; E. D. Cope named them postoptics, and remarked that in Sphenodon they coexist with an orbitosphenoid bone. The proötic has a notch in its anterior lateral margin for the passage of the trigeminal nerve. The opisthotic portion of the petrosal mass is intimately fused with the lateral occipital bones and their paroccipital process, and sometimes, e.g. Tejus, encloses with them many intricate recesses of the middle ear-chamber, which extend also into hollow and swollen thick downward processes of the basioccipital. These cavities of both sides communicate with each other through the cancellous substance of the basioccipital and basisphenoid. There are no Eustachian tubes opening into the mouth through the base of the skull.

The occipital condyle is tripartite, the lateral occipital partaking of the articulation; very rarely, e.g. in Amphisbaenidae (see fig. 22), the basioccipital portion is so much reduced that the skull articulates by two very broad condyles.

The halves of the under jaw are but loosely united, either by ligament only or by an at least very movable suture. The jaw is compound and the numerous constituent bones mostly retain their sutures. Besides the dentary and articular, angular and supra-angular on the lateral side, and the opercular or splenial on the inner side, there lies on the dorsal side the coronoid, six pairs in all. The posterior angle of the jaw