354 Henry L. Bruner 



in Rana fusca. This species therefore, shows a more primitive con- 

 dition in respect to the nasal muscles than the other species, among 

 which Bombinator, at least in the region of the external nares, has 

 experienced the greatest amount of modification. In all the species 

 mentioned, the degree of development of the dilatator naris is deter- 

 mined by the form of the intranasale, which renders the muscle 

 superfluous by the production of a bony support for the plica obliqua. 

 The development of the constrictor naris is also influenced in the 

 same manner. 



5. The Development of the Nasal muscles and of the Glandula 

 nasalis externa in Rana fusca. 



The material which has been used for the study of this develop- 

 ment consists of specimens of Rana fusca, which stand immediately 

 before and after the metamorphosis. 



A very young stage of these muscles I find in a larva thirty 

 millimeters long, whose posterior extremities are seven and a half 

 millimeters long. Here the Anlagen of the nasal muscles consist of 

 closely crowded stellate cells, which already lie in the place of the 

 adult muscles. In this stage the glandula nasalis externals represented 

 by a single sack-like invagination, which is growing inward from 

 the median surface of the plica obliqua. In a larva twenty-five 

 millimeters long and with somewhat longer extremities than the 

 preceding, the muscle Anlagen are composed of spindle-shaped cells 

 with oval nuclei; the muscles appear to be almost functional. The 

 Anlage of the glandula nasalis externa has produced, in this stage, 

 three buds at its inner end. 



A young frog thirteen millimeters long and completely meta- 

 morphosed possesses fully developed nasal muscles, and the con- 

 strictor naris has already spread out in the region of the glandula 

 nasalis externa, which consists now of several tubules with a single duct. 



From the above sketch it will be seen that the nasal muscles 

 of the frog pass through the same sort of development that we 

 observed in the case of the nasal muscles of Triton. 



IV. General Remarks and Conclusions. 



In the preceding pages I have shown that although the general 

 characteristics of the respiration of amphibians are well known, the 



