i86 GENERAL BIOLOGY 



The principal appendages of the enteron. — The lung is 

 here a new feature. As a respiratory sac appended to the 

 alimentary canal, it is peculiar to vertebrates. Among 

 terrestrial animals, most vertebrates are giants, for whom 

 direct absorption of oxygen through the skin would be quite 

 inadequate. Herein is seen the advantage of the lung, 

 which maintains inside the body extensive surfaces that are 

 thin-skinned and always moist. 



The liver is the largest gland in the body, a lobed organ of 

 mottled brownish color, its pointed left lobe partially cover- 

 ing the stomach (in the resupinated position in which the 

 salamander is opened) . Its secretion is collected in a bluish- 

 green sac — the gall cyst, which the right lobe overlies. The 

 cyst is connected by a slender bile duct with the small 

 intestine near the stomach. Compression upon the gall 

 cyst will usually demonstrate that the bile duct opens at 

 this point, by driving the greenish bile down its length, mak- 

 ing the duct visible. The pancreas is an elongated thin flat 

 fatty-looking organ, that lies in the loop formed by the 

 junction of the stomach and small intestine and is covered 

 by the liver except at its posterior end where it touches the 

 intestine. The urinary bladder is the hindmost appendage 

 of the alimentary canal. It is a thin, crumpled sac that lies 

 upon the ventral surface of the large intestine, and opens 

 into the cloaca. Its connection with the excretory system 

 will be discussed later. The thin sheet of membrane in 

 which these digestive organs are slung from the dorsal side 

 of the body wall a.nd through which pass numerous branch- 

 ing incoming and outgoing blood vessels, is the mesentery. 

 The elongate oval reddish body suspended in the mesen- 

 tery behind the stomach is the spleen. 



The lungs are the foremost appendages of the alimentary 

 canal. They spring from the ventral side of the pharynx 

 at the glottis, whose location has already been noted, 



