. Breviora. 1970 PROBAINOGNATHUS JENSENI posterior end of the tooth-row the dentary develops on its inner surface a horizontal ridge which extends back to the posterior end of the bone; below this thickened ridge is a lengthwise excavation in which is lodged the longitudinal "rod" of conjoined bones which support the Fig. 8. Medial view of the jaw of Probainognathiis. The splenial is a long, but thin and slender, element. At its anterior end it takes a small part in the jaw symphysis; it is gen- erally imperfectly preserved, but appears to continue backward, below the ant
. Breviora. 1970 PROBAINOGNATHUS JENSENI posterior end of the tooth-row the dentary develops on its inner surface a horizontal ridge which extends back to the posterior end of the bone; below this thickened ridge is a lengthwise excavation in which is lodged the longitudinal "rod" of conjoined bones which support the Fig. 8. Medial view of the jaw of Probainognathiis. The splenial is a long, but thin and slender, element. At its anterior end it takes a small part in the jaw symphysis; it is gen- erally imperfectly preserved, but appears to continue backward, below the anterior end of the angular, to terminate at a point above the angle of the dentary. In other chiniquodontid genera I have found no trace of a coronoid bone, although it surely existed in vestigial form as a thin internal flake of bone. In Probainognathus, as well, it is absent in most instances. In one specimen, however, the bone is present, but is imperfectly seen (the jaws are in tight occlusion), and I am not sure of its precise outline. As in cyno- donts generally, its function seems to be the provision of a surface (presumably covered with stout epithelium) to play against the ventral process of the pterygoid during jaw movement. Disregarding for the moment the incipient dentary-squamosal contact, articulation with the skull is mediated by a moderately ex- panded area at the posterior tip of the jaw, which is convex dor- sally where it fits into the concavity of the quadratojugal, somewhat concave ventrally to meet the quadrate proper. The lower portion of this articular area is presumably formed by the articular bone. Despite the absence of a suture, it is probable that the upper part of the articulation is formed by the posterior end of the surangular,. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ha
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