25] THE NASAL ORGAN IN AMPHIBIA HIGGINS 25 



the cornu, grows posteriorly along the nasal sac. Unlike Salamandra, how- 

 ever, the planum tectale does not develop from the posterior end of the 

 ethmoidal column, but rather chondrifies laterally from about its middle. 

 Although the planum tectale and the anterior cupola of my later stage 

 resembles in some ways those of both Salamandra and Amblystoma yet the 

 large planum basale and cornu trabeculae of the latter forms, do not exist 

 at any time in Cryptobranchus, both of these structures being greatly 

 reduced. 



SPELERPES BILINEATUS 



The nasal capsule of a Spelerpes larva 15 mm. long (Fig. 18) differs but 

 little from those of the early stages of all Urodeles. The trabeculae (/) are 

 more cylindrical than in Amblystoma, however, and extend forward to the 

 tip of the forebrain, not meeting as yet to form the planum basale. At 

 their anterior ends, each trabecula expands into a triangular cornu, con- 

 siderably smaller than the cornua of corresponding stages of Amblystoma, 

 and, which only partially supports the anterior part of the nasal organ 

 (Fig. 59). Ethmoidal column nor crista trabeculae have not appeared in 

 this stage. 



In a 37 mm. larva (Fig. 19) other parts of the capsule have chondrified, 

 but on the whole the capsule is far more simple than any other Urodele of 

 that age. The cristae trabeculorum (cr i) are well developed and together 

 with the trabeculae form the walls of the cavum cranii. Each crista 

 terminates at the level of the antorbital process, and from its dorsal margin 

 a short process extends anteriorly, which appears to be associated with the 

 development of the ethmoidal column, as described in the later stage. 



From its junction with the crista, each trabecula inclines toward the 

 median line and is united with its mate by a small planum basale (pb), 

 convex upon its dorsal surface and resembling this structure in the second 

 stage of Cryptobranchus. Just anterior to the planum basale the trabe- 

 culae are strongly concave and a prominent ridge has developed along their 

 medial margins, forming a groove for the branches of the nasalis internus 

 of the profundus nerve (Fig. 60). The trabecular cornu is well developed 

 in this stage; its posterior margin extending backwards as a short process 

 to the level of the anterior margin of the planum basale. 



The antorbital processes (pa) are much as in others of the order, arising 

 from the trabecula just beneath the crista, extending laterally a short 

 distance, and then bending anteriorly toward the capsule. 



My oldest stage of Spelerpes is a larva 46 mm. long (Fig. 20). Some 

 additional structures are present, but the capsule is not completely developed 

 and satisfactory comparisons with the capsules of other Urodeles can 

 not be made. 



Opposite the eye, the cristae trabeculorum (cr t) are low; but farther 

 forwards they are higher, their anterior ends being free from the lower 



