53] THE NASAL ORGAN IN AMPHIBIA—HIGGINS 53 
1876) or planum terminale (Gaupp 1893); but from its relation to the 
tectale and the pterygoid, and from its position in respect to the nasal sac, 
the term lamina externa is best used here. Furthermore, it is apparently, 
at least in part, the homologue of the antorbital process of the Urodeles. 
Parker has also used the term prepalatine for this cartilage, which appeared 
to him to be in some way segmented from the more posterior parts; but 
I have no evidence that the lamina externa in Bufo is distinct from the other 
parts, for it appears to develop as a continuum, subsequently uniting to 
the more anterior parts of the capsule. 
From the dorsal margin of the lamina externa, a narrow bar of cartilage 
passes upward, forward and medially over the lateral surface of the nasal 
sac to unite to the lateral margin of the planum tectale, slightly posterior 
to the external naris. This is clearly homologous with the dorsal process 
of Pipa, better known in both groups as the oblique cartilage (Fig. 81). 
The facrimal duct, arising from the eye by two branches, passes forward 
over this oblique cartilage and down through a groove in the lamina 
externa to empty into a lateral diverticulum of the main nasal sac (Fig. 80). 
Anterior to its connection with the oblique cartilage, the lamina externa 
continues forward into the lateral margin of the solum anterius, which 
forms the anterior wall of the cavum inferius, and is evidently developed 
from the cornu trabeculae, together with a dorsal extension of it. It isa 
thin plate of cartilage, bent upon itself, so that it includes in the angle the 
anterior part of the cavum inferius, which contains the more lateral parts 
of the ventral pouch of the nasal sac. More dorsally the solum anterius 
unites to the anterior margin of the planum tectale, its lateral margin 
expanding into the alinasal cartilage, already described. More posteriorly 
and within the capsule itself, is a short cylindrical bar of cartilage which 
extends from the lower margin of the alinasal cartilage to the anterior 
margin of the planum basale, thus separating the main nasal sac from the 
organ of Jacobson. 
A small cylindrical inferior prenasal process, larger than the superior, 
extends forwards and slightly upwards into the intermaxillary glands. 
Below and behind, from the lateral angle of the solum anterius, a short 
process is directed posteriorly which rests beneath the diverticulum of the 
nasal sac, where it receives the lacrimal duct. This process may possibly 
be the tip of the cornu. 
In contrast to Pipa, the capsule of Bufo much more adequately protects 
the olfactory organs; the gaps in its wall being smaller than in that genus. 
In Bufo the choanal fenestra is small and is distinctly bounded by cartilage, 
while in Pipa its boundaries are decidedly indefinite. Again Pipa has no 
circumscribed fenestra naso-basalis. Further differences between the cap- 
sules of the two genera are the greater depth of that of Bufo, correlated 
with a reduction in length, the result being an apparently more complicated 
condition of the anterior parts. 
