14 ILLINOIS BIOLOGICAL MONOGRAPHS [14 



covering to the nasal sac in this region, and which at the same time forms 

 the medial boundary to the external naris. The small band of cartilage, 

 which in the 45 mm. larva connected the tectale to the cornu trabeculae, 

 persists as a flat plate separating the narial opening from the fenestra infra- 

 conchalis, and is pierced by a small foramen for the externus branch of the 

 profundus nerve as it passes to the exterior. 



Anterior to the planum verticale, a band-like cartilage, the lamina 

 medialis (Im) continues forward to the cupola. It is pierced by a single 

 large opening at the base of the prenasal process through which the nasalis 

 internus of the profundus passes to the internasal space. 



In the larva of Amblystoma there is, first, a progressive development 

 which results in a well chondrified nasal capsule, reaching the extreme in the 

 oldest larval stage. With the assumption of adult conditions and the more 

 extensive development of bony structures, this capsule undergoes a marked 

 reduction, chiefly by the resorption of parts. Evidently there is some 

 relationship between the development of the cartilage capsule and the 

 period of metamorphosis, the significance of which will be discussed later. 



SALAMANDRA MACULATA 



In a larva of Salamandra maculata 25 mm. long (Fig. 11), the nasal 

 capsule has chondrified to a stage intermediate between that of the 25 mm. 

 and 34 mm. Amblystomal larvae. The cristae trabeculorum (cr t) termi- 

 nate abruptly just anterior to the region of the eye, from whence the 

 trabeculae pass forward a short distance and then unite to form a broad 

 trapezoidal planum basale (pb). The posterior margin of the planum is 

 parallel to and one-half longer than the anterior, and bears a strong caudal 

 process (cp), which Parker has called the hinder process, lacking in all other 

 stages and in all Urodeles which I have studied, with the exception of a 

 single stage of Cryptobranchus. The dorsal surface of the planum is more 

 concave than that of the corresponding stage of Amblystoma and the 

 ridges formed by the trabeculae are more prominent. 



A broad trabecular cornu (ct) arises from the antero-lateral angle of the 

 planum basale as a thin triangular cartilage, which supports the anterior 

 part of the nasal sac. The lateral margin of each cornu is oblique to the 

 axis of the skull and meets the posterior margin at the level of the anterior 

 boundary of the planum basale; more medially the posterior margin curves 

 backward and fuses with the lateral margin of the planum basale near its 

 middle. 



Parallel to each trabecula, and lying adjacent to the dorsal medial 

 margin of each nasal sac, is the columna ethmoidalis (ce). In this stage of 

 Salamandra, each ethmoidal column is united to the medial margin of the 

 cornu, before the pons ethmoidalis appears; and this fact suggests that the 

 columna does not arise independently here, but is a development back- 



