AND CLASSIFICATION OF THE FOSSIL REPTLLIA. 
219 
(quadrate). I have been unable to find any certain evidence of the presence of the opistb- 
otic in this position. It is stated that the tympanic pedicle is formed by the mastoid, 8 
(squamosal), squamosal, 27 (quadrato-jugal), and tympanic, 28 (quadrate) ; but neither 
in the text nor in the figures is the part taken by each bone defined. I recognize no 
evidence of the quadrato-jugal, and the bone on which the number 28 is placed, 
Plate XXIIL, fig. 1,1 regard as the squamosal, and this bone is also numbered 8 and 27. 
What I regard as the quadrate bone is very imperfectly exposed, and only appears 
as a slender ossification widening distally, placed in front of the distal end of the 
scpiamosal. It is neither described nor figured. Hence, the visible part of the so-called 
tympanic pedicle is formed by the squamosal bone, though, as will be subsequently 
proved in other species, the condylar surface is contributed to by the quadrate bone. 
In the “ Description oiDicijnodon leoniceps ” (p. 32, Plates XXIV.-XXVI.), the author 
regards the occiput as having been crushed into a pair of plates meeting at a right 
angle. This basin-like occipital depression, also found in D. par cheeps and other species, 
seems to me to be natural; for, if pressure had materially approximated the squamosal 
bones in the way implied, it would have obliterated the groove between the parietal 
bones (Plate XXV.), and have otherwise distorted the skull. The form of the condyle of 
the quadrate bone is compared in this species to the distal end of the humerus of a 
Ruminant or the tibia of a Bird. Subsequently it may be sliown that the form of the 
condyle varies with the species. The author states that in this species the squamosal 
descends to near the neck of the outer condyle, and that it extends behind the 
quadrate. The author states that the composition of the tympanic pedicle is clearly 
traceable, but the numbers 8 and 27, placed on its upper part, imply distinct elements, 
which I am unable to find. 
The pair of “ hypapophyses ” below the occipital condyle is said to be formed by the 
basi-occipital and basi-sphenoid ; they are compared to the descending basi-occipital 
process of Lizards, and are supposed to have given attachment to powerful muscles. 
In D. lacerticeps and many Dicynodonts each process is seen to be formed by the (?) 
ex-occipital, basi-occipital, and basi-sphenoid, and to give attachment to the malleus, 
which has not ascended to its position in the skull among Mammals, and extends 
transversely outward to the quadrate bone. The pterygoid, which rests partly on the 
basi-sphenoid, is said to send a process backward, which abuts against the quadrate ; 
this character is regarded as Lacertilian. It will subsequently appear that the 
quadrate may also sometimes send a short pterygoid process inward to meet the 
pterygoid bone ; and that the mode of junction of these bones shows distinctive 
features. The author then describes the long ovate palato-uasal vacuity, which is single, 
but apparently without recognizing the vomer at its anterior margin. Evidence will 
hereafter be given to show that in some other Dicynodonts there are three palatal 
vacuities—one posterior and median in the pterygoid bones, as Sir R. Owen thinks 
possible, and two lateral vacuities divided by the vomer. There is reason to doubt 
whether the ecto-pterygoid (transverse) is found, and the lateral vacuities of the 
Crocodile’s palate are not present. The author compares the inter-palatal vacuity to 
