57] THE NASAL ORGAN IN AMPHIBIA—HIGGINS 57 
causes a shortening of the capsule, which is accompanied by an increase in 
its depth. In front, each trabecula gives rise to a solum anterius which 
forms the anterior wall of the capsule; and at its junction to the tectale 
each solum gives rise to an alinasal cartilage, which supports the anterior 
end of the nasal sac and forms the posterior boundary to the external naris. 
The large naso-basal fenestrae between the medial margins of the anterior 
walls of the capsule and the planum verticale open from the nasal cavity 
to the internasal space much as in Bufo. 
In this stage, the articulation of the lower jaw has moved backward, so 
that the deeply curved muscularis process of the quadrate is more poster- 
ior; and, as a result, the pterygoid has united to the capsule at the point of 
origin of the tectale from the ethmoidal column, the anterior maxillary 
process reaching forward from the junction of the two. 
In a young adult of Rana viridescens (Figs. 85, 86) there has been a 
relative reduction in the height of the verticale, although the proportion 
of breadth to length is approximately unchanged. Anterior to the cavum 
cranii, planum tectale, basale and verticale have fused into a thick plate, 
recalling the association of these same structures in Amblystoma. The 
olfactory foramen (fo) opens obliquely forward from the antero-lateral 
angle of the cavum cranii to the nasal cavity just beneath the foramen 
orbito-nasalis the posterior opening of which lies adjacent to the lateral 
margin of the cranial wall. Lateral to the foramen orbito-nasalis, the 
fused tectale and antorbital curve outward and downward over the choana 
and continue posteriorly into the pterygoid, while anteriorly a small maxil- 
lary process reaches forward midway to the tip of the capsule. 
The nasal sac is completely covered dorsally by the lateral parts of the 
planum tectale which reaches forward to the tip of the cranium, and is 
considerably narrower at the anterior end. At about the middle of the 
tectale, an oblique cartilage bar (oc) extends backward and slightly out- 
ward, ending bluntly near the anterior end of the maxillary process (amp). 
Although unconnected in this stage, these two structures are probably 
the homologue of the lamina externa and the oblique cartilage of the larva. 
The nasal sac opens to the exterior just anterior to the oblique cartilage, 
where the alinasal cartilage, continuous anteriorly into a superior prenasal, 
forms the floor of the naris. Beneath the alinasal, but connected to it, is 
a thick cartilage, the crista subnasalis (cr s) possibly a remnant of the 
earlier solum anterius, although evidence is lacking here. Anterior to the 
crista sub-nasalis is the inferior prenasal process, which extends ventrally 
from the capsule; while directly above it is the fenestra naso-basalis, 
greatly reduced here, and more like that in Hyla. 
