158 H. L. Bruner 



Respiration and Smell in Amphibians. 



All typical amphibians, both terrestrial and acquatic forms, 

 obtain a part of their oxygen supply by means of a bucco-pharyngeal 

 process, in which the respiratory medium is renewed by regulär 

 oscillations of the floor of the mouth. The medium employed in 

 this process is taken through the nasal cavity and is used as the 

 medium of smell. 



In order to establish a correlation between the respiratory mech- 

 anism and the olfactory organ in Necturus and Proteus, it is ne- 

 cessary to review the strueture of the olfactory organ in the dif- 

 ferent groups of amphibians and to describe the various conditions 

 uuder which this organ performs its functious. 



In the Gymnophiona, as shown by Wiedersheim (1879), the 

 Sarasin brothers (1887) and Zuckerkandl (1910), the olfactory organ 

 includes a true olfactory Chamber and a well developed organ of 

 Jacobson, the latter openiug into the former at the choana. As 

 these authors do not describe a mechanism for closing the nasal 

 passage, I have examined adult specimens of Siphonops annulatus 

 in order to determine the character of the nasal openings. In this 

 form the choana is an oval aperture closely supported by skeletal 

 parts and without a closing mechanism. The external naris is sur- 

 rounded by cartilage, which is bent inward behind the opening, so 

 as to form an internal ridge and an external groove. The groove 

 and adjacent space between the nasal capsule and skin are oc- 

 cupied by a smooth muscle mechanism similar to that of the higher 

 urodeles (Bruner, 1897, 1901). It includes but two muscles : a 

 constrictor (m. constrictor naris) and a dilatator (m. dilatator naris), 

 whose fibres are considerably interwoven. 



Adult Gymnophiona are air smellers. I have not been able to 

 examine liviug specimens of this group, but the character of the 

 nasal openings indicates that both incoming and outgoing respiratory 

 currents ass through the nasal cavity. 



In the higher urodeles the nasal organ includes a true olfac- 

 tory cavity and a maxillary cavity, the latter containing the organ 

 of Jacobson. The external naris is closed and opened by a smooth 

 muscle mechanism. The choana is a non-closing cleft, whose median 

 part opens into the true olfactory Chamber, while the lateral part, 

 as suggested by Seydel (1895), provides an open way between the 

 oral cavity and Jacobson's organ. 



