Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/593

1873.] The articular end of each mandibular ramus (Pl. XVI. figs. 1 & 2, ) is broken away: an impression on the matrix shows the vertical diameter of the ramus (fig. 8, ), at the joint with the tympanic, to have been 4$1⁄2$ lines (0⋅009 m.); in advance of this the preserved part rapidly gains depth and gives 8 lines (0⋅017 m.), where it is parallel (figs. 1, 2, ) with the fore border of the orbit. Here a fracture or suture runs from below upward and forward to beneath the hind point or end of the upper jaw (fig. 2, ). If this be a suture, it divides the confluent angular, surangular , and articular elements from the combined splenial and dentary (fig. 2, ). The latter element loses depth as it advances; the fore part is obliquely broken away nearly opposite the broken fore part of the upper jaw. The vertical diameter of the mandibular ramus is here reduced to 5 lines (0⋅010 m.); the portion of ramus preserved on the left side is 2 inches 5 lines (0⋅060 m.) in length; on the right side a corresponding portion of the ramus is preserved, 2 inches 2 lines in length, but with more of the lower border broken away. The course of what remains of the boundary between the dentary (fig. 1, ) and hinder part (ib. ) of the ramus corresponds so closely with that of the left ramus (fig. 2) as to add to the probability that it is a retained suture, or a yielding of the ramus along the line of, perhaps, a partially ossified suture.

The upper border of the mandible beneath the zygoma is moderately convex toward the orbit, but not partially produced as a coronoid process; the ramus here is thin transversely in proportion to its depth, its thickness not exceeding 2 lines.

The upper two thirds of the outer surface of this part of the mandible is feebly convex vertically, and is divided by a ridge due to the subsidence of the flat lower third part of the outer surface. The line of this ridge or subsidence slightly ascends to the suture with the dentary. Prom the part of the suture where such line terminates, a groove (Pl. XVI. fig. 2, f) begins, which traverses the outer surface of the dentary almost parallel with the alveolar border, and at 4 or 5 lines below it; the part of the outer surface of the dentary above the groove is rather more prominent than that below the groove.

The outer surface of both upper and lower beak-bones is sculptured by fine, irregular, subreticulate, seemingly vascular, linear impressions and foramina.

The alveolar border of the preserved hind part of the upper jawbone, an inch in extent on the right side (Pl. XVI. fig. 1). is produced into nine tooth-shaped processes, conical, subcompressed, sharp-pointed, slightly inclined forward. A view of this part of the skull, twice the natural size, is given in fig. 5. The hindmost tooth preserved is but a quarter of a line long, the next is about half a line in length, the third in advance is a little longer, the fourth a little shorter; the fifth (ib. ib. ) suddenly increases to a cone or triangle, 2$1⁄2$ lines along its longer (hinder) side, 2 lines along its shorter (fore) side, and nearly as long across the base, which is confluent with the jaw. The alveolar border swells slightly where it forms