21] THE NASAL ORGAN IN AMPHIBIA HIGGINS 21 



Amblystoma is called the infra-conchalis, separated from the naris by a 

 cartilage bar; while the posterior part of Jacobson's organ rests upon a 

 shelf formed by the prolongation of the cornu. The orbito-nasal foramen, 

 the choanal opening, and the relation of the olfactory organ to the capsule, 

 are features common to both Amblystoma and Diemictylus; and yet the 

 absence of a planum verticale, the greatly reduced planum basale and the 

 complete continuity of internasal space with cavum cranii in the latter 

 form, preclude the determination of close relationships here. 



CRYPTOBRANCHUS ALLEGHANIENSIS 



Practically no work has been done upon the development of the skeleton 

 in the larval stages of Cryptobranchus, although the adult skull and nasal 

 structures have been described by Parker (1876), Wiedersheim (1877), and 

 Wilder (1892). I have studied four stages in the chondrification of the 

 nasal capsule, and although my material lacks some intermediate steps in 

 the process, yet I am able to recognize the method of development and to 

 note some features that may prove interesting from a phylogenetic point 

 of view. 



The early process of chondrification in Cryptobranchus is similar to 

 that in Amblystoma, and my earliest stage suggests the eleven mm. larva 

 of that animal with certain additional features. In a larval Cryptobran- 

 chus two weeks after hatching (Fig. 22), a nasal capsule has not yet formed. 

 The cristae trabeculorum (cr t) are very strong and high, but terminate 

 abruptly near the anterior margin of the eye; while the trabeculae continue 

 anteriorly, turning slightly medially but not meeting to form the planum 

 basale. Each is curved upon its medial surface, which rests against the 

 olfactory lobe ; while anteriorly a ventral lateral expansion of the trabecula 

 is the beginning of the cornu (ct), which resembles Amblystoma, and ends 

 in a blunt process in the surrounding tissue. 



In contrast to the eleven mm. Amblystomal larva, trabecular crests 

 are well developed in this stage of Cryptobranchus; while x>n the other 

 hand, the cornua trabeculorum which are well developed in the young 

 Amblystoma are just beginning to chondrify in Cryptobranchus. Antor- 

 bital processes have not formed, nor is there any trace of an ethmoidal 

 column as in the youngest Amblystoma. 



In a larva five weeks after hatching (Fig. 23), chondrification has ad- 

 vanced in all parts, but the absence of an intermediate stage prevents a 

 definite conclusion as to the origin of certain structures. In general the 

 capsule resembles in many respects that of the 25 mm. Salamandra. 



From the anterior end of the crista, each trabecula inclines toward the 

 median line for a short distance, and then passes straight forward and is 

 united with its mate by a small planum basale (pb) similar in size to that in 

 Triton cristatus. This planum basale differs from that of any Urodele thus 



