The Smooth Facial Muscles of Anura and Salamandrina. 355 



structure and mode of operation of the respiratory mechanism in 

 Anura are somewhat more complicated than hitherto supposed. This 

 complication is especially marked in the provisions which have heen 

 made for the opening and closing of the mouth and external nares. 

 The use of the iutermaxillaria and partes mentales of the dentalia 

 for closing the nares has brought with it problems, whose solution 

 has involved, partly the introduction of new structures, partly the 

 adaptation of already existiug parts to new uses. A new structure 

 which has been introduced to assist in closing the mouth during 

 inspiration is the musculus labialis superior, which seems to be 

 peculiar to the Anura, and is described above for the first time. 

 Among modified parts must be mentioned, a) the hitherto undescribed 

 nasal muscles, which are homologous with the nasal muscles of 

 the Salamandrina and, b) the masticatory apparatus, which has been 

 modified to provide for the protraction of the lower jaw during 

 inspiration. 



The occurrence in Anura of nasal muscles homologous with 

 those of the Salamandrina indicates that the ancestors of the modern 

 Anura possessed a special muscle apparatus for the immediate open- 

 ing and closing of the external nares. This conclusion suggests the 

 question, why this primitive muscle apparatus has been supplanted 

 by the modern mechanism which we find in Anura. To give a 

 satisfactory answer to this question we must take into consideration 

 the fact,' that existing Anura, as a group, display activities of a much 

 higher order than those of the Salamandrina. Higher activities, 

 however, mean increased oxidation and necessitate a more perfect 

 respiratory system. We are therefore, led to inquire, whether the 

 introduction of the new contrivance for the closing and opening of 

 the external nares has increased the efficiency of the respiratory 

 mechanism of the modern Anura. It seems quite evident that such 

 is the case. Through the use of his masticatory muscles and 

 the submentalis for the closing of the external nares, the 

 frog has substituted the quickly responsive striated mus- 

 culature for the slower smooth nasal muscles of his an- 

 cestors. The gain to the modern Anuran may be appreciated, if 

 we compare the energetic respiratory movements of the frog with 

 those of his more humble relative, the salamander. The intro- 

 duction of a new mechanism for the opening and closing of 

 the external nares of Anura has had for its object then 

 simply a change of musculature; to secure this end nature 



