50 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
showing a side view of the skull and mandible of Xenophrys monti- 
cola is copied). The Mento-Meckelian element in the Frog is also 
represented and described in Parker and Bettany’s ‘ Morphology of 
the Skull,’ fig. 45, p. 171, London, 1877, in which it is stated to be 
derived in part from Meckel’s “ cartilage-rod,” and in part from the 
remains of the ‘inferior labial” cartilage. 
But the Mento-Meckelian mandibular element can be traced lower 
in the vertebrate scale ; for Dr. A. Giinther figures it in Aspidorhyn- 
chus Fisheri (‘ Introduction to the Study of Fishes,’ fig. 146, p. 369), 
naming it here the ‘“ presymphysial bone” (as noticed by Dollo). 
In Protopterus, the Meckelian cartilage extends beyond the dentate, 
Fig. 4.—Cranium of Aspidorhynchus Fisheri. (Original from 
specimen in the British Museum.) 
coalescing with its fellow in the median line, to form a stout 
azygos plate, the free edge of which is set with small pointed ° 
processes singularly suggestive of likeness to Jguanodon. The Men- 
to-Meckelian bone is recognizable also in Sturio andin Ama. Thus 
it is present in Lepidosteoidei, Dipnor, Chondroster, and Amioider, in 
four therefore of the eight suborders under which Dr. A. Giinther 
arranges the numerous genera of the once dominant order of the | 
Ganoid fishes. 
i 
‘ 
This mandibular element is, however, not restricted to the lower — 
vertebrates, for it exists in the human embryo, in which it was dis- 
covered by "A. von Kolliker, and by Callender, in whose paper in the 
Phil. Trans. 1869 it is floured (pl. xii. fig. 6a). In a footnote 
referring to this paper, W, K. Parker calls ‘it the “Interior inter- 
maxillary element,” Phil. Trans. :p.'200, vol. clxi. , 
‘This wide distribution of the Mento-Meckelian element appears to 
me to afford strong support to the homology of the presymphysial 
bone of Jguanodon offered by Dollo. The time at my disposal will 
not permit me to examine in detail the many interesting features of 
the skull in Jguanodon, discovered or confirmed by M. Dollo. IJ can 
allude to two only :—the edentulousness of the premaxillary, which 
alone would be sufficient to demonstrate its generic distinctness 
