12 ILLINOIS BIOLOGICAL MONOGRAPHS 12 
the length of the planum verticale, so that one-half of the entire capsule lies 
anterior to this median vertical plate. The width of the verticale is also 
reduced by one-half to accommodate the lateral development of the olfactory 
organs which now lie much closer together. The anterior surface is widely 
concave, its dorsal margin overhanging the ventral, thus forming a partial 
roof over the intermaxillary glands. 
The planum ‘ectale (pt) now covers the entire dorsal aspect of the nasal 
ac and extends from the region of the choana to the tip of the capsule 
where it has united to the anterior margin of the cornu trabeculae, forming 
the cupola (Fig. 9). This area is pierced by five small foramina. Four of 
these are in an oblique quadrilateral, the fifth, much larger, lying behind 
the others. Of the four, the anterior three foramina are for the branches 
of the nasalis internus which are distributed to the dorsal part of the snout; 
while the lateral foramen passes a branch of the profundus from the capsule. 
The larger posterior gap contains no nervous structures and apparently is 
the beginning of the resorption of the cartilage roof of the capsule. The 
medial surface of each capsule is marked distally by a small prenasal process 
(pnp) at the base of which is the foramen nasalis internus (fii), above 
described. On the dorsal surface of the capsule is a sixth small foramen for 
a branch of the profundus of the fifth nerve, the result as before, of the 
extension of the cartilage around the nerve. 
The antorbital process (pa) has now united to the lateral posterior 
margin of the tectale, a condition foreshadowed by the close association of 
these parts in the earlier stages, thus inclosing a large foramen between the 
posterior margin of the tectale and the basal part of the antorbital. This 
is the foramen orbito-nasalis (fom) into which the caudal part of the nasal 
sac extends, and through which the nasalis internus of the fifth nerve enters 
the capsule. Lateral to this foramen, the united elements of the antorbital 
and tectale are directed obliquely forward, covering the lateral aspect of the 
olfactory organ. A branch of the profundus nerve and a blood vessel 
pierce this plate by two foramina just posterior to its connection with the 
caudal] extension of the cornu trabeculae (Fig. 9). 
As in the earlier stages, the organ of Jacobson rests upon the caudal 
extension of the cornu which extends more posteriorly, and has partially 
united to the fused tectale and antorbital. This union of the cornu to the 
posterior tectale has resulted in the formation of a new foramen, the infra- 
conchalis of Gaupp (fez 7c), through which the anterior part of the organ of 
Jacobson extends to the laterally enveloping tissue (Fig. 46, jo). Thus 
this organ rests upon a shelf formed by the cornu trabeculae, while its 
anterior end extends through the foramen. This infra-conchalis is separ- 
ated from the large lateral narial opening by the bar, which in the 45 mm- 
larva connects the cornu trabeculaeand the tectale. A deep groove occur- 
in the lateral wall of the planum tectale which leads to the posterior bound- 
