CLASSIPICATION, AND PHYLOGENY OF THE DINOENITHID^. 397 



Anomalopteryx, Emeus, and Mesopteryx ; in JDinornis it is inclined, sloping outwards 

 from its lower border. The anterior end of the dorsal edge presents a distinct alveolar 

 groove, like that on the premaxilla ; the posterior end is produced into a rough 

 irregular coronoid process for the insertion of the temporal muscle. 



The form of the symphysis naturally follows that of the premaxilla, being broad in 

 Binornis and Emeus, narrow in Pachyornis, Mesopteryx, and Anomalopteryx. The result 

 of this is that the entire mandible is U-shaped in the two first-named genera, V-shaped 

 in the others. The symphysis itself is almost horizontal, and shows considerable 

 variation in its proportional length. Its ventral or outer surface is marked with a broad 

 ridge, like that on the premaxilla, very well marked in Binornis, less so in Pachyornis, 

 Mesopteryx, and Anomalopteryx, and only just raised above the surface in Emeus. 



On the inner surface of each ramus, 1-2 cm. in advance of the articular cup, is the 

 dental foramen for the mandibular nerve ; it perforates the bone, appearing externally 

 at the hinder end of a deep groove along which the nerve runs, entering the ramus, 

 between the two laminae of the dentary, at its anterior end. Two small foramina lie in 

 the groove, one near its lower border, the other towards the anterior end of its dorsal 

 border ; they perforate the bone and probably transmit nerves to the tissues on the 

 inner surface of the jaw. 



Another pair of foramina, apparently for the symphysial branches of the mandibular 

 nerve, lie in the posterior edge of the symphysis, usually just in the re-entering angle 

 between the rami. They generally lie side by side, occasionally one above another ; in 

 some cases they are united at their origin into a single foramen, and in one instance 

 have moved forwards to near the anterior end of the symphysis. 



Emeus has, of all genera, the stoutest and most coarsely built jaw, Anomalopteryx 

 coming nearest to it in this respect. The mandible of Binornis, in spite of its strong 

 symphysis, has comparatively weak rami, but the most delicate lower jaw of all is that 

 of Mesopteryx casuarina. 



In young specimens the mandible readily divides into three parts : a symphysial 

 portion, containing the ankylosed dentaries and the splenials, which latter are separate 

 in still younger skulls ; and the posterior portions of the two rami, each containino- the 

 articular, angular, supra-angular, and coronary (fig. 7). None of the specimens I have 

 seen show the latter group of bones in the separate condition, but in a young 

 mandible of Anomalopteryx didiformis the outlines of the angular and supra-angular 

 can be traced where they overlap the articular. The splenial is well shown in a 

 mandible of Emeus crassus ; it extends from about the level of the dental foramen 

 forwards to within 4 mm. of the symphysis. Lastly, in the type specimen of Binornis 

 torosus, in which the splenial is absent, the articular is continued forwards into a 

 cylindrical tube of bone lying immediately mesiad of the dental foramen and evidently 

 representing the superficially ossified proximal end of Meckel's cartilage. 



VOL. xiii. — PABT XI. No. 4. — October, 1895. 3 l 



