A Contribution to tlio Anntoiiiy of Siren laccrtina. 685 



A small muscle serves to draw back one of these valves, thus 

 giving the animal the power of expiration. 



LÉON Vaillant (0. 315) describes a small muscle of the external 

 nasal opening under the name of abducteur de la mâchoire 

 supérieure, which surrounds the nares and is inserted into the 

 ossicle at the side of the praemaxillary (Cuvier's rudimentary maxillary). 

 This muscle I have not been able to tind, which may perhaps be due 

 to a very imperfect series of sections of this region. Fischer, however, 

 states an equally negative result. With regard to the ossicle first 

 mentioned, it has been spoken of only by the two authors just named, 

 CuviER and Léon Vaillant. If it be as given in Cuvier's figure (E), it 

 closely resembles the maxillary of Siredon, which in the Axolotl form 

 is nearly as rudimentary, becoming of much more importance in the 

 transformed Amblystoma. Owing to the failure of several sections in 

 this region, I have been unable to investigate it. 



C. Comparative study of the nasal cavity. 



The complex relations above described are essentially different 

 from those met with among the other Perennibranchs, and as long as 

 we assign to Siren the low position generally given it by the syste- 

 matists, they remain totally aberrant and unaccountable. But if we 

 consider it a degenerate larval form of a once higher animal, we find 

 that the perplexities are only such as are always met with in the case 

 of degenerate types which, wandering back into a lower class, have 

 yet retained many traces of their once higher development. 



Accordingly, if we do not attempt to compare the nose of Siren 

 with those of the externally similar Proteus and Menohranchus, but 

 seek for analogies among the higher Urodelans, we will find essentially 

 similar relations. As a type of the simplest Amphibian nose we may 

 take Proteus or Menohranchus where the cavity is in the form of 

 a simple depressed oval, without outward folds or accessory cavities. 

 The structure here is fish-like, the mucous membrane still exhibiting 

 Schneiderian folds. The next stage may be found in Triton, where, 

 lateral to the principal cavity, we find an accessory chamber extending 

 into the maxillary region, very much depressed but possessing a lumen 

 and lined with olfactory cells. In Plethodon, Spelerpes, and allies, at 

 the superior boundary between the principal and accessory cavities, 

 a partition projects into the interior, making the separation of the 

 two cavities more pronounced. Siredon represents the next staarc 



