File:The Quarterly journal of the Geological Society of London (13889303337).jpg

48 '- PROCEEDINGS OF THE GEOLOGICAL SOCIETY.
Fig. 1. — Side view of Cranium o/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. Pox, 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 Hypsilopliodon^ has long been in my own collection ; and recently
Prof. E. D. Cope has figured this same element in Biclonius, a
member of the Hadrosauridae, the Transatlantic representatives of
our Iguanodontidas. 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 an.^ other Sauria. What is this ? In Dielonius, D.
mirabilis (fig. 2^:.s), 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 presymphysien " together
with the " Dentary " in Iguanodon^ 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 inferieures." A. Ecker, as noticed by
Dollo, figured these in 'Die Anatomie des Erosches' (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 Erog," Phil. Trans. 1871, and this-
author's later memoir " On the Structure and Development of the