VERTEBRATA. 71 



manner as in snails, and the sepias: it form a small mesentery and 

 a rudimentary epiploon, and it presents the remarkable peculiarity 

 of its cavity communicating with the surrounding medium by the 

 tvyo small openings, placed at the side of the anus. 



AMPHIBIA. 



These animals, like the fishes, are predaceous in their habits, 

 and swallow their food without mastication. The whole of them 

 have prehensile teeth in the palate ; salamanders have them in both 

 jaws, frogs in the upper only, and the toad and pipa in neither, but 

 in the toad two small transverse rows exist behind the posterior 

 nares. The teeth in the proteus nearly resemble those of the sala- 

 mander, but in the siren they are arranged in a quincunx order as 

 in many fishes, and amount nearly to two hundred. The salivary 

 glands are absent in the aquatic, and merely rudimentary in the 

 terrestrial amphibia. In the toad and perennibranchiate amphibia 

 the tongue is short, thick, and fleshy, but in the frog it is 

 long, free, bifid, covered with papillae and mucous follicles, as in 

 reptiles The short, dilatable, fleshy oesophagus, leads to a narrow, 

 transversely elongated stomach, muscular in it parietes, and over- 

 lapped by a large bilobate liver with a distinct gall bladder. In 

 the young tadpole of the frog the almentary canal is very long, the 

 intestine which is narrow and coiled, measures ten times the length 

 of the space from the mouth to the anus, but after the metamorphosis 

 has occurred, and that the mixed food of the tadpole is changed for 

 that of a more nutritious nature, as snails, worms, ccc, the canal 

 becomes gradualy shortened to one fourth of its former length. The 

 duodenum has transverse folds like valvular conniventes, and the 

 short, wide colon ends in the cloaca, together with the openings of 

 the genital and urinary organs. The mucous membrane forms 

 longitudinal folds in the proteus, the triton, the pipa, and the sala- 

 mander ; transverse folds in the froo-, and quadrangular cells in 

 the hyla. A small pyloric valve exists in the toad and pipa, and 

 the valve of the colon is distinct in the frog, the triton, and the 

 hyla. The liver, the spleen, and the pancreas are found in all the 

 amphibia, varying in shape according to the form of the animal. 

 Thus we perceive in the lower orders of amphibia, an evident 

 approach in their digestive organs to those in fishes, in the great 

 number of teeth, shortness and width of oesophagus, absence of 

 fundus to the stomach, want of distinction between large and small 

 intestine, and the magnitude of the liver. But in many we discover 

 an approximation to the higher vertebrata, in having fewer teeth, 

 an elongated tongue, fundus to the gastric cavity, distinction between 

 large and small intestine, absence of pyloric and colic valves, and 

 the development of transverse folds in the duodenum. 



