OCR Text |
Show 1895.] LORIUS FLAVOPALLIATUS AND PSITTACUS ERITHACUS. 391 of the inferior margin of the ramus instead of one of about 60° as in P. erithacus. On the outer surface of the ramus there are in both species some small foramina, and a rather conspicuous one in P. erithacus. In that species also there is a considerable oval vacuity, or defect of ossification, at about the middle of the ramus dorso-ventrally, the middle of the vacuity being beneath the post-coronoid process. In L. flavopalliatus, however, the ramus is here entire but somewhat depressed or concave in this region. This depression is limited behind by a ridge which runs obliquely downwards and forwards from the articular process to the ventral margin of the ramus. This is only represented in P. erithacus by a prominence which runs downwards and forwards from the articular process for about half the breadth of the ramus. In P. erithacus a small foramen opens beneath the prearticular process at about one-fourth of the dorso-ventral diameter of the ramus from its dorsal margin. In L. flavopalliatus it opens a little behind that process and nearer the dorsal margin. Its external surface towards the angular process is slightly concave in both species, rather more so in L. flavopalliatus. In L. flavopalliatus the inner surface of each ramus presents two elongated concavities separated by a ridge. At its anterior end this ridge curves sharply upwards, being also there most prominent, and approaching near to the coronoid process. Just behind its upwardly bent part a conspicuous foramen leads into the substance of the mandible. At its posterior end this ridge joins the outer margin of the larger articular surface for the quadrate, at tbe same time bounding externally a small but deep fossa which is situated outside the front part of that surface. In P. erithacus the conditions are similar save that the ascending anterior part of the ridge is the most conspicuous and ascends completely to the coronoid process, and that the foramen behind it is less conspicuous, opening on the front margin of the defect of ossification (which interrupts the internal longitudinal ridge); when the defect of ossification is smaller, the foramen opens beneath it. In both species the small foramen beneath or near the prearticular process opens into the superior longitudinal concavity of the inner surface of the ramus. In both species also the larger articular surface for the quadrate is in the form of an antero-posterior, nearly straight groove. This groove is broadest at its anterior end in P. erithacus, but hardly at all broader there in L. flavopalliatus. O n its inner side there is a small surface of bone, broadening gradually backwards, at the hinder end of which is a foramen. This is the innermost part of a subquadrate bony process, the internal articular process (id), which projects nearly horizontally inwards and supports the outer part of the longitudinal articular groove. The smaller and superior articular surface for the quadrate (sa) is on the inner side of the somewhat everted coronoid process. It is nearly straight antero-posteriorly, but strongly convex dorso- |