'46
J. W. HULKE ON AN OS ARTICI7LARE,
Fig. 3. — Inner View.
a. Tympanic surface. c. Ascending process.
Fig. 4. — Under Surface.
a. Under surface of articular face. b. Outer surface.
c. Sutural surface for angular bone.
This foramen is present in all Mr. Fox's specimens, and may be looked on as constant in this type of articular bone. I find it also in the Hypsiloplio don's mandible. A perforation in a bony element, and not a space between the angular, surangular, and dentary pieces, this foramen does not correspond to the large oval opening in the mandible of extant and extinct crocodilians, but rather to the fora- men, sometimes double, present in the surangular element in some extant lizards. (Such foramina are to be seen in Iguana tuberculata, 672 a, and Sphenodon, 662 a, Mus. Roy. Coll. Surg.)
In its whole preserved extent the upper border of the vertical plate is a thin, non-articular, smooth, rounded lip. From in front it gradually and gently rises to a short distance behind the large foramen just described, where it reaches its greatest height ; and thence it descends in a sinuous S- curve, the first bend of which is steep and abrupt, the second bend shallow and open. In front of the tympanic joint the whole inner surface of the vertical plate is non-articular, but less smooth than the outer surface of the same part. It is much hidden by the sheet rising from the front of the tympanic surface, with which it forms the sides of a large and deep hollow, in the fresh state presumably filled with the persistent
