NUTRITION IN ANIMALS 



155 



air-breathing Vertebrates the gill slits persist merely as 

 transient embryonic reminders of evolutionary history, their 



FIG. 88. Diagram of the alimentary canal and its derivatives in Man. a, 

 mouth; b, salivary glands; c, pharynx, showing the embryonic position of five 

 pairs of gill pouches, the second pair probably giving rise to the tonsils, and the 

 third and fourth to the thym us glands; d, thyroid gland ; e, trachea; /, thymus 

 gland; g, lungs; h, oesophagus; i, diaphragm the muscular partition between 

 the thorax and abdomen; j, liver; k, gall bladder; I, stomach; TO, pancreas; 

 n, small intestine; o, large intestine; p, vermiform appendix; q, rectum leading 

 to exterior by the anus. 



function being taken over by an outpocketing of the ventral 

 wall of the pharynx into the body cavity, which forms the 

 LUNGS. Thus, even in Man, the respiratory membrane which 



