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Show OF THE SKULL. 216 ON 'l'IIE STHUOTURE '· b no dou bt a b ou t t he premaxilloo (Pmx), r the thus th re can e I .. -toothed vomers (Vo). The . (M. ) nd the two arge ruax. J.l la f th.v ' pao steri.O r nares b et ween the last-named. bones and p rtwn o . cti'on with the relations of the <Pl) taken rn conne th bon s I . of the skull sufficiently defines t th prefronta regiOn ' . latt r 0 0 t f Pl· while Pt connected with the 1 1 t' e charac er o ' ' . . t lO pa. a Ill h d and terminating on the Inner side of 1 t . n the one an ' ' pa a 1nes 0 the mandibular suspensori. um on t.h e other' corresponds as dis- tn.l C. tl J WI't h t'i le pteryaoo ids of the higher Vertebrata. Fig. 87. 'artil:. crinous rani urn of Rm 1 e cule_nta. A, from abo•e; B, from below Fig. 7.-The :tg (utter Duge-).-y, the gtrdle bone. th th THE SKULLS OF AMPHIBIA. 217 This arch clearly answers to the sub-ocular arch of the Lampreys and to the sub-ocular cartilage of the Chimreroids and Lepidosiren, and corresponds with the palato-quadrate, hyomandibular, and symplectic cartilages of the embryonic osseous fish ta.ken together. The distal end of this cartilaginous pedicle commonly presents a larger or sn1aller ossification of its substance, which represents the quadrate ·bone. Now, the problematical bone (z) lies on the outer side of the pedicle, and I was at one time· inclined to think that it represented the hyomandibular bone of. osseous fish-being largely led to that impression by the great size of the hyomandibular and the comparative minuteness of the quadrate in the Conger and the Muroonoid fishes. But the h yomandiLular is au ossification in the cartilage of the suspensorium, not a membrane bone. The bone has been compared with the tympanic, but the tympanic membrane has a special and distinct supporting ring in the Frogs. It has been identified, again, with the squamosal, but it lies too far down on the outer side of the pedicle for t.hat bone. Tracing the changes of form in this bone (which is very constant in the Amphibia) downwards to the Menobranchus and Siren, its resemblance in these perennibranchiates to the bone (F) of Lepidosiren becomes very striking; and I am disposed to identify it with that bone, which, as I have stated above, has much resemblance to the pre-operculum of osseous fishes. The mandible of Amphibia is commonly composed of three pieces-a dentary, an angular, and an articular. The latter, always continuous with Meckel's cartilage, may itself remain persistently cartilaginous. The skull of the tadpole, before ossification has commenced, presents a cartilaginous base, in which the notochord terminates in a point: immediately behind the pituitary fossa. At the sides, the basal cartilage expands into two oval auditory capsules, and in front passes into the trabeculm cranii, which embrace the membranous floor of the pituitary fossa, and reunite in the broad ethmo-vomerine cartilage. The apex of a sub-ocular arch, connected, behind, with the auditory region of the basis cranii, and, in front, with the prefrontal region, furnishes an articular |