ON RHAMPHORHYNCHUS BUCKLANDI 145 
= 
first alveolus. The vertical diameter of the ramus is least between 
the fifth and sixth alveoli, where it amounts to about .jths of 
an inch. <Anteriorly the vertical diameter increases to the second 
alveolus, where it measures half an inch. 
The upper edge of the rostrum is nearly straight. Its obliquely 
broken end has an oval section, measuring 3th of an inch vertically 
by sith horizontally. The specimen has been broken through im- 
mediately behind the third alveolus; and the section of the left 
ramus at this point has the form of an elongated oval, half an inch 
long by one-tenth of an inch wide. The plane of the ramus is 
directed a little outwards, as well as upwards; and its walls are 
extremely thin. The fractured surface of the matrix further ex- 
hibits a sectional view of the right ramus, whose plane is similarly 
inclined, so that, while the lower edges of the two rami are only }th of 
an inch apart, the upper edges are more than 4rd of an inch distant. 
The outer surface of the left ramus exhibits, nearer the lower 
than the upper margin, and extending from the level of the fourth 
alveolus to that of the anterior margin of the second, a slight hori- 
zontal ridge. This ridge terminates abruptly in front, and seems 
to have constituted the outer wall of a vascular canal; for a delicate 
groove is continued forwards from it, and vanishes upon the outer 
surface of the bone. Other canals of a similar character are seen 
upon the rostrum. These vascular ramifications are so similar to 
those observable upon that portion of a bird’s bony jaw which is 
covered by the horny beak, that I should have been inclined to sus- 
pect the existence of a similar horny sheath to the mandible, even 
had not Von Meyer demonstrated its existence in Rhamphorhynchus 
Gemming?. 
The sutures which should limit the different components of the 
jaw are very indistinct. The best-marked runs obliquely from below 
the articular cavity, upwards and forwards, to a point half an inch 
in advance of the anterior edge of that cavity, and 3th of an inch 
below its upper margin. Here it ends in a minute pit filled with 
matrix. Another less distinct, apparently sutural, line is traceable 
from immediately behind the last alveolus backwards, to a point 
nearly midway between the pit just mentioned and the anterior 
edge of the articular cavity. Here it is joined, at an acute angle, 
by another indistinct line coming from the pit; and the two enclose 
a triangular tongue of bone. I suspect that this belongs to the 
dentary element, and that the pit answers to the foramen visible 
on the outer face of the Crocodile’s jaw, between the supra-angular, 
angular, and dentary elements. 
VOL. II L 
