26 ILLINOIS BIOLOGICAL MONOGRAPHS [26 
trabecula and reaching farther forward than before (Fig. 21). Anterior 
to the crista, each trabecula turns more abruptly toward the median line for 
a short distance, and then anteriorly; uniting by a very small planum bas- 
ale, which in this stage is flat and level, with the dorsal surfaces of the 
trabeculae. 
Anterior to the planum basale, the trabeculae continue forward, sep- 
arated from each other by a narrow internasal space; each expands distally 
into a small cornu which supports the tip of the nasal organ. Arising from 
the dorsal and medial margin of each trabecula, just anterior to the planum 
basale, is a small process which extends backward a short distance along the 
medial margin of the nasal sac. This process is the further development 
of the medial ridge of the trabecula in the 37 mm. stage; and from its 
relation to the nasal organ, it must be the beginning of the columna 
ethmoidalis, whose further history is unknown (Fig. 61). 
I regret that I have no older stages showing the farther chondrification 
of the capsule; thus preventing a careful comparison with other Urodeles. 
In general, however, Spelerpes seems to indicate a retarded growth in all 
parts. In corresponding ages of other Urodeles, there is a much more 
complete capsule than in Spelerpes. 
I have not observed the free anterior extension of the crista in any 
other Urodele, with the exception of Amphiuma; and judging from its 
relation to the nasal organ and trabecula, it would appear as though this 
process is the posterior beginning of the ethmoidal column. In other 
words the columna ethmoidalis in Spelerpes may arise by the fusion of two 
parts independent of each other; the anterior part from the medial margin 
of the cornu, the posterior part from the anterior margin of the crista. In 
no other Urodele, as far as I have seen, does the column arise in just this 
way; however the early development of the crista trabeculae in Crypto- 
branchus and the lateral development of the tectale from the middle of 
the ethmoidal column, ledds me to conclude that in Cryptobranchus the 
column arises, as in Spelerpes, from two distinct independent outgrowths. 
The small planum basale is similar to that in Cryptobranchus, but the 
larger cornu in the 37 mm. stage is more like that of Amblystoma. My 
material does not show the formation of the planum verticale, but it 
evidently does not arise as a dorsal growth from the planum basale, but 
more probably by medial growths from the ethmoidal columns; thus in 
this particular, approaching the condition in Salamandra. 
The complete absence of intermaxillary glands, the close approxima- 
tion of the capsules anterior to the planum basale, as well as the small size 
of the latter, are points of similarity to Cryptobranchus, which, on the 
evidence of larval characters alone, I believe Spelerpes more closely resem- 
bles. 
