LIASSIC FORMATIONS. 
49 
In the left ramus of the mandible two of the large anterior laniaries are in place ; one, 
answering to the second in PI. XVII, 2 ', projects across the diastema between the second 
and third tooth above ; in size, shape, and curvature, it resembles the second upper laniarj, 
close to which it terminates. The next mandibular tooth is larger, less curved, and crosses 
the middle of the interval between the third and fourth upper laniaries. The tooth (lO 
displaced beneath the mutilated fore part of the mandible, I take to be the foremost of 
the mandibular series and suppose that its point would naturally project across the interval 
between the first and second of the upper teeth. The fourth laniary appears to be more 
displaced ; its base or root, with a lateral depression, is shown behind the fifth tooth of 
the minute serial teeth, and the crown passes obliquely backward on the inner side of 
that of the sixth upper laniary, by which it is concealed. Of the serial teeth, with pointed 
crowns from half a line to a line in length, about thirty may be reckoned occupying an 
alveolar extent of 2 inches, 9 lines. 
At the hind part of the left mandibular ramus, here exposed, three longitudinal 
ridges define two vacuities, of which tlie inferior may be natural. The upper one seems 
more plainly due to loss of the thin outer plate of bone extended between the upper two 
ridges. The proportions of the ramus closely accord with those of the first-described 
specimen. The fore part of the mandible is too much mutilated for useful comparison. 
The dentition of DimorpJiodon, as displayed by the second specimen of skull, consists, 
in the upper jaw, of laniaries with wide intervals, eleven in number on each side ; in the 
lower jaw, of four, if not five, laniaries implanted at the fore part of each ramus of the 
mandible at intervals corresponding with three of the four anterior laniaries above ; then 
follows the long series of close- set and minute pointed teeth. The difference of dentition 
as compared with the first specimen (PI. XVII) is, in the upper jaw, in the additional 
small laniary or cuspidate tooth at the back part of the series in that specimen. In the 
lower jaw there does not seem to be any noteworthy difference in the number, kinds, and 
position of the teeth. The longest laniaries are included between the second and fifth in 
both jaws : the upper laniaries after the fourth become small and straight. 
At the first view of the framework of the huge head of our Liassic dragon one is 
struck with the economy of bony material and the purposive skill with which it has 
been applied or disposed, so as to give strength where resisting power was most required. 
The lodgment of the poorly developed brain enlists a miserably small proportion of the 
skull ; the cranium proper, or brain-case, is relegated to an out-of-the-way corner, so to 
speak, and there it is almost concealed by the projections for joints or muscular 
attachments. The orbits accord with the large eyes given to this volant and swift-moving 
Reptile. 
One can conceive no necessary interdependent relation between the wide external 
bony nostril (>*) and the organ of smell, nor be led to conjecture that the tegumentary 
inlets to the nasal chamber were larger than is usual in Reptiles. 
The main purpose of the head is for prehension of prey. The jaws are produced far 
7 
