18 ILUNOIS BIOLOGICAL MONOGRAPHS [18 



the antorbital process, thus completing the foramen orbito-nasalis {fon) 

 through which the nerves of the nasal region enter the capsule. A small 

 foramen in the tectale, just opposite the pons ethmoidalis conducts a 

 branch of the profundus nerve from the capsule; while the larger oval gap 

 in the anterior tectale, separated from the external naris by a narrow bar is 

 one of the gaps described by Born in the adult. 



The lamina medialis {Im) forms the medial wall of the capsule, anterior 

 to the foramen olfactorius, and is continuous with the tectale and the cornu 

 trabeculae (Fig. 56), thus bounding the internasal space. The floor of the 

 capsule is formed by a large trapezoidal cornu trabeculae which extends 

 back to the level of the pons ethmoidalis where it forms the anterior margin 

 of the choana. Its lateral margin unites to the lamina externa, forming the 

 boundary to the naris, over which the naso-lacrimal duct passes to the nasal 

 sac, as in Amblystoma and Salamandra. Posterior to its junction with the 

 lamina externa, each cornu terminates in a small posteriorly-directed pro- 

 cess, which supports the organ of Jacobson; although, as in Salamandra, a 

 fenestra infra conchalis does not yet exist. At the anterior end, the floors 

 of the two capsules approach each other, and at the extreme medial tip of 

 each is a small prenasal process (/>»/»), probably the homologue of that 

 structure in both Amblystoma and Salamandra. The nasalis internus of 

 the profundus nerve leaves the capsule through the foramen at the base of 

 the prenasal process. 



The nasal capsule of the older larva of Triton cristatus (35 mm. long) is 

 intermediate between the 28 mm. stage and that described by Born (1877), 

 in which large gaps have developed. In this stage there has been a reduc- 

 tion in the length of the capsule, most of which occurs at the anterior end, 

 so that the width is greater in proportion to the length than in the earlier 

 larva. The relation of the forebrain to the nasal sac is much as before; 

 but in the adult, according to Born, all olfactory structures are entirely 

 anterior to the central nervous system. The planum basale and the pons 

 ethmoidalis are much as in the earlier stage, except that the pons is now 

 much farther anterior than is the basale, while the foramen olfactorius and 

 ethmoidalis are larger than before (Fig. 17). 



Cartilage has formed around the branch of the profundus nerve which 

 supplies the organ of Jacobson, cutting off a smaller foramen adjacent to 

 the foramen orbito-nasalis (Fig. 17, 57). Just anterior, and slightly 

 lateral to this foramen, the lamina externa has united to the caudal exten- 

 sion of the cornu trabeculae thus outlining the foramen infra-conchalis, as 

 in Amblystoma, through which the organ of Jacobson protrudes from the 

 capsule. 



Further description of this capsule is unnecessary, with the exception 

 of the cupola (c), which now encloses the anterior parts of the nasal sac, so 

 that now the external naris is entirely lateral. The lamina medialis (/w) 



