31] THE NASAL ORGAN IN AMPHIBIA— BIGGINS 31 



throughout the entire urodelan order, as primitive, would be unjustified; 

 but, the greatly retarded process of chondrification, the absence of cristae 

 and cornua trabeculorum, together with the entire separation of the roof 

 of the capsule from the other parts, may be explained in either of two 

 ways; Necturus has either descended from some more specialized Urodele, 

 or, as the retarded process of chondrification would suggest, it may repre- 

 sent a neotenic condition of some form, like Spelerpes. 



AMPHIUMA MEANS 



The first of the three capsules of Amphiuma studied, is that of a larva 

 still within the egg, in which the chondrocranium is very incomplete, 

 resembling in many ways the larva described by Kingsley (1892), and 

 figured by Winslow (Fig. 18, 1898). 



Each trabecula, from the crista forwards, inclines, at first gradually, 

 and then somewhat more abrupt, toward the median line; the two uniting 

 to form a small rectangular planum basale (pb, Fig. 29), which supports 

 the olfactory lobes. Anterior to the planum, each trabecula continues 

 forward a short distance, and then expands into a triangular cornu, concave 

 upon its dorsal surface to support the anterior part of the olfactory sac. 

 The cornua are separated from each other by a deep and narrow inter- 

 nasal space, resembling that of Spelerpes, the Urodele, the larva of which 

 most resembles the early Amphiuma. 



The cristae trabeculorum (cr t) are well developed and extend forward 

 to the base of the antorbital process {pa), which in Amphiuma is directed 

 obliquely forward from the trabecula, rather than at right angles to it as in 

 other Urodeles. The anterior margin of each crista trabeculae is con- 

 tinued forward as a cylindrical bar along the medial dorsal margin of the 

 nasal sac. At the level of the anterior end of the antorbital process, the 

 bar runs forward and outward and passes obliquely over the nasal organ, 

 giving rise to a short process just dorsal to the nasal sac, and continuing 

 outward and downward to the lateral surface of the sac where it turns 

 directly forward and runs along the lateral surface of the sac nearly to the 

 level of the planum basaie. Hay (1890) speaks of this bar as the rudi- 

 mentary nasal capsule, while Winslow (1898) describes it as projecting 

 forward, outward and downward, but without the small dorsal processes 

 present in my stage, and which help to explain the later modifications of 

 the capsule. In its origin from the trabecular crest, this bar, which 

 probably contains elements of both ethmoidal column and tectal cartilage, 

 recalls the process in Spelerpes, extending forward from the anterior margin 

 of the crest, which was interpreted as the posterior end of a developing 

 columna ethmoidalis. 



Olfactory foramina do not exist, but each olfactory nerve passes over 

 the trabecula just in front of the crista trabeculae, where the nasal organ 

 and the olfactory lobe are very close together. 



