| OCR Text |
Show 178 DR. R. BROOM ON TIIE [Feb. 17, consists of two complete mandibles in articulation with the posterior half of the skull. The lower jaw lies almost at right angles to the axis of the skull, and the upper cervical vertebrae have been to some extent protected by passing down between the two rami. The skull consists of the practically complete occiput W'ith both temporal arches in almost perfect condition, and with most of the parietal and sphenoidal regions well shown. Though the sutures unfortunately are not distinct, the occiput is so well preserved, practically without distortion, that I think it worthy of being figured. The vertebrae so far as preserved consist of the proatlas, atlas, axis, and the 3rd and 4th cervical vertebrae. The atlas (at.) consists of a well-developed arch and a distinct hypapophysis (h.at.). The arch is partly broken in the middle, but must have borne considerable resemblance to that of the mammals. It differs in having had a distinct posterior zygapophysis (z.at.) for articulation with the small anterior zygapophysis of the axis (z.ax.). The zygapophysis of the left side is well preserved, but that of the right has been broken off. On the right side the outer part of the arch is continued backwards as a well-developed bony process or rib (r.at.). It is probable that the process is really a rib, but I have been unable to find a suture between it and the arch. On the under surface, what appears to be part of the rib of the left side is seen lying by the side of the body of the axis (r.at.). The well-developed hypapophysis is also well seen. It appears to have had only a ligamentous connection with the arch of the atlas. In front of the arch of the atlas, and lying in the hollows formed above and outside of the occipital condyles, are the two portions of the proatlas. Each consists of a short bony arch with a well-developed process passing upward and outward from its outer end. The axis is well developed, and bears considerable resemblance to that of Cynognathus. The spine forms a very large flattened crest. In the specimen it is somewhat damaged, but there is probably not a great deal missing. In front, the spine passes forwards over the arch of the atlas, and possibly forms an articulation with it as in the Monotremes. Between the anterior part of the spine and the odontoid process is the small anterior zygapophysis (z.ax,). The odontoid process (o.]i.) is well developed, and on the right side it is seen articulating with the arch of the atlas. On the under surface the body of the axis is seen, as also a part of the odontoid process in articulation with the hypophysis of the atlas. On the upper surface, near the posterior end of the centrum, on the right side is a portion of the rib of the axis. The 3rd and 4th cervicals present no features worthy of any special remark. Remains of ribs are seen in connection with each. In the type specimen of Trirachoclon hannemeyeri there are preserved and well shown the t\vo portions of the proatlas, the |
