.The Smooth Facial Muscles of Aniira and Salamandrina. 337 



superior maintains a steady tension during respiration and 

 changes little or none with the various phases of the process. 



2. The Mechanism for Closing and Opening the External Nares 



in Rana. 



a. General Anatomy of the region adjoining 

 the External Nares. 



The anatomy of the nasal region of Anura has been repeatedly 

 described and a full account of the structure may be gathered from 

 the works of Ecker and Wiedersheim (16), Parker (39), Born (4), 

 Ctaupp (19 and 22) and others. In the following description I shall 

 use Rana fusca Roesel as a type, by means of which the details 

 given below have been verified. (Compare Figs. 8 to 15, Pis. XVII 

 and XVIII.) 



In each of the two nasal cavities of Rana fusca two distinct 

 regions may be distinguished, a rostral complex region which consists 

 of three blind sacks, and a caudal simple one which is undivided. 

 The blind sacks of the anterior region all communicate behind with the 

 posterior division and include a dorsal cavum superius, a horizontally 

 flattened cavum inferius and a cavum medium, which occupies a 

 lateral position and lies in part between the cavum superius and 

 the cavum inferius. These different subdivisions of the nasal cavity 

 are inclosed in a cartilaginous nasal capsule which possesses on each 

 side a roof (tectum nasale), a floor (solum nasale), and a short lateral 

 wall, the last of which forms the lateral boundary of the cavum 

 medium. Above the cavum medium the wall of the nasal cavity is 

 supported in part by an oblique blade of cartilage, the cartilago 

 obliqua (Fig. 8, PI. XVII and Figs. 11 to 14, PI. XVIII) which arises 

 from the anterior portion of the roof of the nasal capsule, extends 

 caudo-laterally and terminates in a sagitally placed plate (planum 

 terminale). This plate presents below a caudal free angle and a 

 rostral angle which is bent inward until it stands approximately at 

 right angles to the body axis (see P.t., Fig. 14, PI. XVIII). In front 

 of the cartilago obliqua lies the spoon-shaped cartilago alaris previously 

 described. The large fenestrae which occur in the nasal capsule of 

 Triton alpestris are all represented in Rana. The apertura naris 

 externa evidently corresponds to the anterior end of a fenestra 

 rostro-lateralis, which is in part separated from a fenestra dorsalis 

 by the cartilago obliqua. Owing, however, to the fact that the 



