564 BE. A. GUNTHER’S DESCRIPTION OF CEEATODUS. 
PLATE XXXIV. 
Structure of the Skull , compared with that of Dipterus. 
The cartilaginous parts are coloured blue ; figs. 1-3 are f- the nat. size. 
Fig. 1. Upper view of the skull, with the facial cartilages preserved. 
Fig. 2. Upper view of the same, after removal of the greater part of the osseous covering 
and of the temporal muscle, to show the cartilaginous skull. 
Fig. 3. Lower view of skull ; the soft parts surrounding the upper jaw have been pre- 
served, to show the position of the nostrils. 
a. Scleroparietal. 
1). Ethmoid. 
c. Frontal. 
d. Tympanic lamina. 
e. Infraorbital ossifications. 
f. Infraorbital cartilage ; f . facial cartilage. 
g, g , g. Vacuities within the cartilage. 
h. Operculum (removed in fig. 3). 
i. Part of scapular arch. 
k. Prgeoperculum. 
l. Pterygo-palatine. 
m, ml. Foramina for the 1st and 2nd rami of nervus trigeminus, 
oi. Nostrils. 
o. Basale. 
p. Cartilaginous roof of gill-cavity. 
q. Os quadratum. 
r. Tubercle for hyoid. 
s. Suspensory pedicle. 
t. Foramina for 3rd ramus of nervus trigeminus. 
u. Foramen for carotis posterior. 
v. Vomer, with pair of vomerine teeth. 
iv. Foramina for nervus vagus. 
x. First rib. 
x 1 . Cartilaginous tubercle attached to the first rib. 
Fig. 4. Lower view of the skull of Dipterus , of the natural size, from a specimen in the 
Geological Museum in Jermyn Street, No. ~L 
1. Pterygo-palatine. 
0. Basale. 
01. Excavated place where the two nostrils were situated. 
v. A pair of round holes in which the vomerine teeth were fixed. 
Figs. 5 and G. Horizontal section of the anterior (fig. 5) and posterior (fig. 6) portion 
of the sclero-parietal bone, magn. 216. 
a. Medullary canals. 
