346 Henry L. Bruner 



of the external nares is possible after tlie submentalis has been 

 eliminated. 



From the description of the nasal muscles of Rana fusca it has 

 already been seen that these muscles do not take an immediate part 

 in opening or closing the external nares. The function of the dilatator 

 naris may be best understood by recurring to the description of the 

 plica obliqua. This fold, which limits the movement of the cartilage 

 alaris when the external naris is closed, spans the great arch formed 

 by the anterior margin of the cartilago obliqua (see Figs. 8 and 9, 

 PI. XVII). The contraction of the dilatator naris gives tension to the 

 plica obliqua and thus provides for the caudal end of the cartilago 

 alaris an elastic support. A somewhat different function is performed 

 by the constrictor naris, whose contraction will produce the following 

 effects: a) tension of the soft part of the median margin of the nasal 

 opening; b) stretching of the epithelium of the anterior and lateral 

 surfaces of the plica obliqua, and c) retraction of the caudal wall 

 of the vestibule of the cavum superius. The last named function is 

 to be attributed to the lateral part of the muscle, which thus keeps 

 the caudal wall of the vestibule of the cavum superius drawn back 

 and out of the way of the cartilago alaris. Thus also the entrance 

 to the cavum superius in kept open during the intervals between 

 the movements which close the nasal opening. The plica obliqua and 

 the soft median margin of the external naris are parts which come 

 in direct contact with the cartilago alaris when the naris is closed; 

 tension of these parts must greatly facilitate the secure closing of 

 the external naris. 



In addition to the above functions, the relation of the constrictor 

 naris to the glandula nasalis externa of Rana suggests that the 

 contraction of the muscle must facilitate the discharge of the secretion 

 of the gland. Such a function agrees with what we have already 

 learned in regard to the nasal muscles of the Salamandrina. 



From the above it is evident, that although the mm. 

 constrictor naris and dilatator naris of Rana no longer play 

 the leading role in closing and opening the external nares, 

 they nevertheless perform functions which facilitate the 

 closing and opening of these apertures; they have in fact 

 become parts of the complicated mechanism, which, in the 

 Anura, has assumed the function which the nasal muscles 

 themselves once performed. 



The question whether the nasal muscles of Rana contract each 



