Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/239

 is, it measures 1*5 in. in length ; and the palatine surface has a width of 0-25 in. in front and 0-55 in. behind. The section of the bone is trihedral, the outer face of the trihedron being somewhat concave, the inner convex from above downwards ; the anterior half of the upper edge is thin and broken ; the posterior half is a comparatively broad, longitudinally grooved, narrow surface. Along the bottom of the groove lie three apertures, which are probably vascular foramina ; and other such foramina lie on the inside and on the outside of the ridge into which the anterior half rises. One of the foramina on the inside is the commencement of a canal which traverses the base of the ridge longitudinally.

Pig. 1. — Left palato-maxillary o/ Hyperodapedon.

A. From the inside. D. From below. B. From the outside. C. From above. E. From behind.

The posterior half of the oral surface of the bone presents two faces, which are inclined towards one another at an obtuse angle ; the wide valley which they include ends abruptly in a sharply cut narrow groove. On the outside of this groove lies a single row of fifteen teeth, anchylosed with the edge of the outer wall of the valley. The anterior eleven of these are worn down to a level with the bony substance of the jaw ; the twelfth and thirteenth have their points ground away, while the fourteenth and fifteenth are entire and sharply pointed.

The inner wall of the valley presents two parallel series of teeth — one on the middle, and one on the extreme inner edge. Traces of fourteen or fifteen teeth can be discovered in each series. Those of the middle series are, all but the very hindmost, worn down to the