460 
PEOFESSOE OWEN ON THE DICYNODONT EEPTILIA. 
rounding support, which have kept the lower jaw in its natural connexions with the 
tympanic pedicle. 
In the breaking up of the hard rock in which this fossil has been imbedded, the right 
maxillary, tympanic, and zygomatic arch have been removed ; the fore part of the upper 
jaw, from the beginning of the sockets of the canine tusks, and the corresponding end 
of the lower jaw, are also broken away. The length of the remaining portion of the 
skull now exposed is 1 foot 6 inches ; but this is somewhat more than it would natm’ally 
be, owing to the left half of the broad occipital region (Plate XXII. 4, ss) having been 
bent backward from the transverse to almost the longitudinal position, in the line of the 
skuU’s axis, and this with so little disturbance of the connexions of its elementary bones 
as exemplifies, with other similar condition of the skull, the gradual operation of the 
disturbing force, and the condition of surrounding support that has made the pressure 
act upon the brittle fossil as if it had been a plastic material. For, after close observa- 
tion and reflection upon all the appearances presented by this fossil, I infer that the 
cosmic movements affecting the matrix have operated after the sediment in which the 
dead body of the old reptile was buried had become, with its contents, hardened into 
stone. 
After careful removal of the matrix from the remaining petrified bones of the right 
side of the skull, the occipital tubercle ( i ) was worked out in its whole length : it pro- 
jects from the lower plane of the basioccipital (h) to the extent of 1 inch 8 lines, and 
from the foramen magnum (f) about 1 inch 4 lines ; the vertical diameter of the base 
of the tubercle is 1 inch 6 lines ; it slightly expands to its articular convexity. The 
right side of the tubercle having been broken away, the compact or close granuloid 
texture of the bone is here displayed. 
The occipital hypapophyses (h) are 2 inches in length ; the left paroccipital ( 4 ) expands 
to a breadth of 5 inches, where it abuts against the broad masto-tympanic pedicle (2s). 
An extent of 6 inches by 4 inches of the smooth posterior surface of this singularly ex- 
panded lamelliform bone is here preserved. The small vacuity (a) between the par- and 
exoccipitals has been converted into a foramen by the meeting of extensions of ossifica- 
tion from 2 to 4. The foramen magnum (/), naturally of a vertically oval form, is here 
made narrower by the slow lateral squeezing of the occiput ; its long diameter is 1 inch 
4 lines. The lower angle of the superoccipital ( 3 ) is preserved, making an extent of the 
well-ossified occipital plane reaching to 4 inches above the occipital tubercle. 
The removal of the outer part of the maxillar}^ and the zygomatic arch has brought 
into "sdew part of the interorbital septum, and the upper and outer part of the bony 
palate ; structures that have not been shown by previous specimens of Dictjnodon. 
The descending cranial plate of the frontal, where it forms the inner wall of the orbit 
and the rhinencephalic continuation of the cranial cavity, is shown at n, Plate XXII. 
The basisphenoid (ih. 5 ) is short and deep, and sends out a process uniting with one 
from the pterygoid, to abut against the tympanic pedicle. 
The presphenoid (ib. g) projects forward as a compressed plate 10 lines in vertical dia- 
