19] THE NASAL ORGAN IN AMPHIBIA— HIGGINS 19 



is pierced by a small foramen for a branch of the nasalis internus of the 

 profundus nerve, the main part of which leaves the capsule through the 

 foramen in front of, and at the base of the prenasal process. At the anter- 

 ior end of the floor of the capsule is a small gap which I believe to be the 

 beginning of the larger gap described by Born for the adult. 



It is impossible to be certain of all the homologies between the nasal 

 capsule of Triton and that of Amblystoma, without the early stages. Born 

 (1877) has described the process of chondrification, but has shown no figures 

 for his early stages. Terry (1906) says: "The development of the cartilag- 

 inous nasal skeleton of Amblystoma is comparable in many respects with 

 the processes in Triton as described by Born." Born says nothing of an 

 ethmoidal column which chondrifies independently and then later becomes 

 associated with the trabecula; on the contrary he says: "Bei den Tritonen 

 die Knorpelkapseln der Nasenhohlen durch directes auswachsen der 

 Trabecel gebildet werden." The lamina medialis, planum tectale and 

 lamina externa would thus be formed by a continuous growth from the 

 trabecula; while the many gaps in the capsule would arise by interruptions 

 in the process. 



Throughout its development, Amblystoma never has a fenestra eth- 

 moidalis completely outlined, and yet it is distinctly present in both stages 

 of Triton; and Born says: "Dieser Internasalraum ist bei Triton cristatus 

 und taeniatus, niemals durch eine knorpelige Wand von der Schadelhohle 

 geschieden, sondern immer hautig gegen dieselbe abgeschlossen." 



In larvae of Salamandra, Pelobates and Rana, the fenestra ethmoidalis 

 is complete, being bounded by cartilage upon all sides, but is closed in the 

 adult; while it persists throughout life in Triton and Diemictylus. 



DIEMICTYLUS VIRIDESCENS 



The nasal capsule of a 38 mm. larva of Diemictylus viridescens resembles 

 in many ways that of the 35 mm, Triton cristatus. In both, the two cap- 

 sules are united by a very small planum basale, the only connection between 

 them even in the adult Diemictylus, which lacks the pons ethmoidalis; 

 so that internasal space and cavum cranii are continuous cavities. The 

 small planum basale {ph) supports the anterior part of the telencephalon 

 which reaches forward into the internasal space ; so that olfactory lobes and 

 intermaxillary glands overlap in this animal (Figs. 14, 53). 



The antorbital process {pa) has united to the posterior margin of the 

 tectale at two places, thus outlining two small fenestrae the inner of which 

 is the foramen orbito-nasalis {fo n) for the nasalis internus of the profundus 

 nerve; while the outer conducts the externus branch of the profundus, 

 which supplies Jacobson's organ. 



Anterior to these foramina, the united elements of the planum tectale 

 and the antorbital process completely cover the dorsal and lateral parts of 



