164 



BIOLOGY. 



[BOOK TI. 



existing in the inferior animals, are also found on the buccal 

 orifice, in form of a cupping-glass, of the cyclostomes. The 

 amphibians have likewise analogous organs on the edge of their 



jaws. 



In the fishes, the ganoids and the teleostians, there are teeth on 

 the jaws, the palatal bones, the vomer, the hyoid bone and the 

 bronchial arcs ; the selacians have none except on the jaws.' 

 (Fig. 10.) 



A 



Fio. 9. 



Digestive tube of fishes. A, gobius melano- 

 stomus, B, salmon; o, oesophagus ; v, sto- 

 mach ; i, median intestine ; ap, pyloric 

 appendices ; r, rectum. 



Fro 10. 



Buccal opening of the pdro- 

 myzon marinus, with corneous 

 teeth. 



The teeth of fishes, of amphibians, of reptiles fall and are 

 renewed during the whole of life. 



The three divisions of the digestive tube, properly so called, 

 grow gradually more perfect in proportion as the animal rises in 

 the hierarchy of the vertebrates. 



In fishes the first part of the digestive tube has direct 

 continuity to the stomach without difference of diameter (Fig. 9). 



