48 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
Fig. 1.—Side view of Craniwm of Iguanodon bernissartensis, Dollo. 
(After Dollo.) 
incontestable evidence ot undisturbed natural articulation. I had 
often myself in bygone years pondered over a detached, mutilated 
example in the collection of the late Rev. W. Fox, now in the British 
Museum, but was quite unable to identify it with any element in 
the vertebrate skeleton then known to me. A similarily formed 
detached bone bedded in a block of clay, together with a mandible 
of Hypsilophodon, has long been in my own collection ; and recently 
Prof. EK. D. Cope has figured this same element in Diclonius, a 
member of the Hadrosauride, the Transatlantic representatives of 
our Iguanodontide. Thus in three Dinosaurs, members of closely 
allied herbivorous genera, there is now known to be present in the 
mandible an azygos element, till lately unrecognized, and not known 
to exist in any other Sauria. What is this? In Dielonius, D. 
mirabilis (fig. 2 ps), Prof. Cope names it “ Dentary”; but apart from 
the obstacles which the structure of the mandible in this Dinosaur, 
as described and represented by Cope, offer to the reception of this 
identification, the coexistence cf the *‘ os présymphysien ” together 
with the “ Dentary” in /guanodon, negatives this determination of 
its homology. M. Dollo, with commendable reserve, suggests that it 
may be the morphological equivalent of the ‘* Mento-Meckelian ” 
elements present in the mandible in Batrachia, termed by Prof. P. 
Albrecht ‘‘intermaxillaires inférieures.” A. Ecker, as noticed by 
Dollo, figured these in ‘Die Anatomie des Frosches’ (fig. 22. p. 40), 
Braunschweig, 1864. They are well shown in several of the plates 
illustrating Prof. W. K. Parker’s memoir “‘On the Structure and 
Development of the Skull of the Frog,” Phil: Trans. 1871, and this- 
author’s later memoir “On the Structure and Development of the 
Skull in Batrachia,” in Phil. Trans. 1881 (from which fig. 3 m.m.. 
