41] THE NASAL ORGAN IN AMPHIBIA—HIGGINS 41 
of the ethmoidal column in Cryptobranchus, for in the five weeks larva it 
already unites the medial margin of the cornu to the crista; but judging 
from its relation to the capsule, and in its complete separation from its 
mate, these structures resemble those of Spelerpes in which the anterior 
part of the columna arises from the medial margin of the cornu and grows 
posteriorly along the nasal sac. Further, the anterior prolongation of the 
dorsal crista in Spelerpes, interpreted as the posterior part of a developing 
column, may also exist in Cryptobranchus, although conclusive evidence 
on this point is lacking. 
In the 25 mm. Salamandra larva, the anterior end of the column is 
connected to the cornu trabeculae much as in Cryptobranchus; and yet 
the expansion from its posterior end, forming a small tectale prior to any 
connection with the crista, suggests an independence of the ethmoidal 
column, like that of Amblystoma. Although the dorsal crests of Salaman- 
dra develop along with the columna ethmoidalis, the two do not unite until 
a later stage, thus the posterior part of a developing column is lost in all 
Urodeles above Spelerpes. In Amblystoma, on the other hand, the eth- 
moidal column and the cornu trabeculae are chondrified independently of 
each other. Ina 13 mm. larva, I have described a few cartilage cells above 
the medial margin of the cornu of the left trabecula only. This is the first 
appearance of an ethmoidal column which subsequently grows posteriorly 
along the median dorsal margin of the nasalsac. The fact that I observed 
these cells as chondrifying, at first, upon one side only, has no especial 
significance; but in the independent chondrification and the complete 
development of the ethmoidal column from in front backwards, prior to 
any association with the trabecula, Amblystoma differs from any other 
Urodele, except Necturus in which the independently chondrified ethmoidal 
column never unites to other parts of the capsule. Thus in the 20 mm. 
stage of Amblystoma, completely developed columnae ethmoidales parallel 
the trabeculae from their anterior tips to the choana; but do not unite to 
any crista, which here is greatly retarded in its appearance, not developing 
until the 25 mm. stage is reached. 
The ethmoidal column in Amphiuma is more like that of Cryptobran- 
chus and Spelerpes in the development of the posterior parts; there being 
no evidence of an anterior part of a column in the youngest larva studied. 
Somewhat as in Spelerpes, the anterior portion of the crista continues 
forward into a cylindrical bar along the medial margin of the nasal sac, and 
from its relation to other parts, as well as its position, it must be regarded 
as a columna ethmoidalis. As in Cryptobranchus, it gives off laterally a 
small process which may be homologized with the tectale, which then turns 
anteriorly, forming the lateral wall of the capsule, the lamina externa. 
In all Urodeles studied, the planum basale is formed by a fusion of the 
trabeculae in the middle line of the skull; and in some forms, this plate, 
