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Show 1874.] PROF. T. H. HUXLEY ON MENOBRANCHUS. 189 otics behind, while, in front, the vomers underlie it on each side. Its anterior extremity is truncated, and slightly concave forwards. 5. The vomers (Fo) are much elongated, flattened, broader behind than in front, and have a sigmoid curvature, which is especially manifested by their inner edges. As the vomers come into contact only by their anterior extremities, while their inner edges diverge from one another backwards, there is left between them a wide space, increasing in breadth posteriorly, which is occupied, for the greater part of its extent, by the parasphenoid, but, in front of the truncated anterior termination of this bone, by a part of the chondrocranium. A series of teeth is set along the outer edge of each vomer; and its posterior excavated extremity articulates with the palatine bone. 6. The parietal bones (Pa) which are broad and flat, cover over the greater part of the epiotic and pro-otic bones. They meet in a median sagittal suture, which is about half as long as the whole skull. Anteriorly, each parietal bone presents three processes. The innermost of these (Pa1) is the proper continuation of the bone; uniting with its fellow, it gives rise to the anterior half of the sagittal suture, and extends forwards, as a long triangular tongue, which is interposed between the two frontals (Fr). The second (Pa2) and third (Pa3) processes start from a common root. The inner, very long and slender, runs along the outer edge of the frontal bone, widening a little as it goes, and ends at the posterior boundary of the olfactory foramen (I). The third process (Pa3) is short, passes downwards and outwards, and rests, in a manner to be described presently, upon a cartilage connected with the suspensorium*. 7. The frontal bones (F?-), separated behind by the conjoined parietals, unite, in front, in a long frontal suture, and terminate, anteriorly, in pointed processes, which are received between the ascending processes of the premaxillary bones. Between the latter and the olfactory foramen, each frontal is continued into a plate of bone (Fr1), which lies on the sides of the snout. The anterior, pointed, extremity of this plate fits in between the ascending process of the praemaxilla and the vomer, while its posterior prolongation passes, below the olfactory aperture, to the cartilaginous antorbital process of the skull. 8. A quadrate ossification (Qu) of irregular form, occupies the distal end of the cartilaginous suspensorium. 9. The palato-pterygoid (PI. Pt) is a flattened plate of bone, rounded and spatulate in front, where it articulates with the excavated posterior end of the vomer ; truncated behind, where it underlies the suspensorium. 10. The pramaxilla (Pmx). These are relatively strong bones, each composed of a horizontal "body" bounding the gape in front, and of a strong ascending process, which passes back on to the top of the skull, at an acute angle with the body of the bone. The " body " tapers off to a point posteriorly ; and, in the specimen the skull of * Professor Owen considers that this process represents "the so-called columella of Lizards" (I. c. p. 116). |