302 



THE VITAL FUNCTIONS. 



the water by the muscular action of its sides. 

 The forms assumed by the respiratory organs in 

 this class are almost infinitely diversified, while 

 the general design of their arrangement is still 

 the same. 



As we rise in the scale of animals, the respira- 

 tory function assumes a higher importance. In 

 Fishes the gills form large organs, and the con- 

 tinuance of their action is more essential to life 

 than it appears to be in any of the inferior 

 classes : they are situated, as is well known, on 

 each side of the tliroat in the immediate vicinity 

 of the heart. Their usual form is shown at g g, 



Fig. 360, where they are represented on one side 

 only, but in their relative situations with respect 

 to the auricle (d), and ventricle (e), of the heart; 

 the bulbus arteriosus (b), and the brancliial ar- 



M 



