330 Henry L. Bruner 



meters long the constrictor naris and dilatator naris accessorius are 

 functionally developed; here, however, as in the earlier stage, the 

 dilatator naris is still wanting. This muscle was first observed as a 

 weak rudiment in a specimen one hundred and fifty-six millimeters long. 



The glandula nasalis externa of the axolotl is represented, in 

 a specimen eighty millimeters long, by a single invagination, which 

 extends caudalward between the Anlage of the constrictor naris and 

 that of the dilatator naris accessorius. In the axolotl of one hun- 

 dred and two millimeters there are two tubules present in the last 

 mentioned region, and these have extended still farther caudalward 

 in the specimen one hundred and fifty-six millimeters long. Beside 

 the above there is, in the last mentioned specimen, a single tubule 

 which penetrates the body of the constrictor naris. 



From the above study of the development of the nasal muscles 

 and gland we may sum up the following results: — 1) The smooth 

 nasal muscles of Triton and Amblystoma arise in place from 

 mesenchyme cells. 2) The glandula nasalis externa and the 

 nasal muscles develop e at an equal pace and become function- 

 ally mature at about the same time. 3) The time of maturity 

 of the nasal muscles and gland probably precedes, by a short 

 interval only, the beginning of adult life. The large size of 

 Amblystoma when the nasal muscles and gland first appear is ex- 

 plained by the peculiar development of this species which attains 

 an enormous size before entering the adult state. 



III. The Closing of the Mouth and External Nares in Anura. 



It has been shown above that in the Salamandrina the closing 

 of mouth and nares is controlled by wholly independent mechanisms; 

 in Anura, on the contrary, the opening and closing of the external 

 nares and the closing of the mouth are controlled by the lower jaw. 

 The absence of special muscles for the immediate opening and 

 closing of the nares of ßaua has been shown by Gaupp (20 and 21), 

 who has also given an excellent account of the mechanical arrange- 

 ment which has supplanted the muscles. But Gaupp's work still 

 leaves open the question, whether, after all, muscles homologous with 

 those of the salamanders, but with a changed function, may not 

 exist in the Anura. The question acquires additional interest from 

 the fact, that, as I have elsewhere (8) stated, such muscles occur 

 also in the Crocodilia. 



