21G 
PROFESSOR H. G. SEELEY OR THE STRUCTHRE, ORGANIZATIOR, 
edentulous Turtle-like mandible and pre-maxillary ; (2) the expanded vertical occipital 
plate, which is compared to that of Crocodiles; (3) the brain-case is only two-thirds 
the breadth of the inter-orbital space, and in its small size suggests the lowest 
Amphibians ; while (4) the two tusk-like teeth are only paralleled among Mammals. 
One of the distinctive Dicynodont characteristics is the junction of the par-occipital 
and sphenoid with the tympanic, near to the broad slightly convex condyle. 
The bones which are identified in the skull are :—the basi-occipital, ex-occipital, par- 
occipital, sur-occipital, basi-sphenoid, mastoid, parietal, post-frontal, mid-frontal, vomer, 
pre-frontal, nasal, lachrymal, inter-maxillary, maxillary ; the malar was thought to be 
blended with the maxillary ; the palatine, dentary, articular, splenial, angular, coronal, 
zygomatic, tympanic. 
In 1859, Professor Huxley made an important contribution to knowledge of the 
Dicynodont skull in his memoir on the Ptychognathus MurrayiP By making trans¬ 
verse vertical sections of the skull, the remarkable median vertical longitudinal plate 
which extends forward from the brain-case w'as discovered. The pre-sphenoid is said 
to be united with the basi-sphenoid by an oblique suture. Anteriorly it becomes the 
inter-orbital septum, and passes into the ethmo-vomerine plate or nasal septum. This 
expands interiorly and unites with the maxillary. The palatine bones are found to be 
attached to the pre-sphenoid below the anterior border of the orbits, and, passing 
forward into the maxillary, define, with the ethmo-vomerine septum, the two posterior 
nares. The nasal passages of Birds make a much closer approximation to the con¬ 
dition in Dicynodon than is found in the Monitors. And it is observed that the 
manner in which the palatines and pteiygoids are connected with one another and 
with the pre-sphenoid is extremely Bird-like. 
In 1859, Sir Bichaiid Owen made full descriptionst of species which indicated 
the existence of other genera, named Ptychognathus and Oudenoclon, and elucidated, 
in a more perfect way, many characters of the skull which were indicated in the 
original figures and descriptions of Dicynodon. In the same memoir the genus 
Galesaurus was defined, which afterwards became the type of a distinct family, and 
eventually was placed in another order of Reptiles. 
In the same year. Sir Richard Owen contributed to the Reports of the British 
Association for the Advancement of Science, a memoirj; “On the Orders of Recent 
and Fossil Reptilia and their Distribution in Time,” in which the order Anomodontia is 
defined for the first time. It then comprised three families ; Dicynodontia, founded on 
Dicynodon and Ptychognathus; Cryptodontia, founded on Oudenodon; and Gnath- 
odontia, fouuded on Rhynchosaurus. The third family does not appear to have been 
sustained, for, in a later writing,§ Rhynchosaurus is grouped under the Cryptodontia. 
* ‘ Geol, Soc. Quart. Journ.,’ vol. 15, p. 649, on Dicynodon Murmyi. 
t Ibid., vol. 16, 1860, p. 49; and ‘ Ann. Nat. Hist.,’ vol. 4, 1859, p. 77. 
t ‘ Brit. Assoc. Report,’ Aberdeen, 1859, p. 153. 
§ ‘ Palaeontology,’ 2nd edition, 1861, p. 263. 
