10 ILLINOIS BIOLOGICAL MONOGRAPHS {10 
Another cartilage arises from the lateral side of each trabecula, behind 
the choana, and the anterior margin of the cristal connection of the trabec- 
culaand column. This has been called by the German writers, the palatine 
process; but it has no relation to the palate or the palatine bone, and is 
better called by another name, frequently used for it, the processus antor- 
bitalis (pa). It extends laterally about as far as the cornu, and is destined 
to form a part of the posterior wall of the nasal capsule. 
As yet there are no distinct olfactory foramina, but the olfactory nerve 
leaves the forebrain at right angles to its median axis and passes into the 
capsule through the large gap between the trabecula and the column, just 
anterior to the crista trabeculae. 
In a 34 mm. larva (Figs. 5, 6)the process of chondrification which formed 
the pons ethmoidalis of the 25 mm. stage, has continued ventrally and 
posteriorly, so that the bridge has joined the planum basale and has extend- 
ed back to about the level of the planum tectale of the previous stage. 
The result of this is the formation of a large median wall to the cavum 
cranii, the only openings left being the olfactory foramina which pass into 
the capsules at the lateral margins of this wall. From conditions which 
occur in other Urodeles this median mass is best called the planum verticale, 
although it is much thicker than in Amphiuma and the Caecilians. As will 
be seen in the sequel, this planum verticale may be defined as the cartilage 
connecting the nasal capsules of the two sides, beginning as a median dorsal 
pons ethmoidalis from the two columnae and then extending down to join 
the planum basale. The anterior margin of the planum verticale (pv) is 
deeply excavate, and together with the medial walls of the nasal capsule, it 
bounds the V-shaped internasal space in which the intermaxillary glands 
lie. The lateral margins of the verticale slightly extend over the medial 
margins of the nasal organs from the olfactory foramen to the tip of the 
capsule, thus forming the anterior part of the planum tectale, which is 
pierced by a small opening (fn) through which the ramus nasalis internus 
of the fifth nerve passes into the internasal space. Thus the planum 
verticale is a compound structure formed from the ethmoidal bridge and 
the columnae ethmoidales, uniting ventrally with the planum basale. 
The posterior parts of the planum tectale (f#), which began in the last 
stage (25 mm.), now forms a broad curved plate which covers the caudal 
half of the nasal organ, and extends forward from the crista trabeculae to the 
level of the anterior margin of the foramen olfactorius. Laterally it extends 
nearly to the level of the gap between the caudal extension of the cornu and 
the antorbital process; the posterior margin of the tectale is oblique, its 
antero-lateral margin is slightly arcuate, while in front it is produced into a 
small conical process (Figs. 5, 6). 
The expanded cornua trabeculorum (c?) do not differ greatly from those 
of the preceding stage. The lateral margin of each cornu is slightly arcuate 
