The Development of the Frog 49 



The lungs arise from the narrow part of the 

 digestive tract which lies just back of the wide 

 anterior end or pharynx. A longitudinal fold 



CH 



FIG. 18. LONGITUDINAL VERTICAL SECTION THROUGH THE HEAD 

 AND ANTERIOR PART OF THE BODY OF A TADPOLE ABOUT THE TIME 

 OF APPEARANCE OF THE HIND LEGS. LENGTH OF TADPOLE, 12 MM. 

 X 14. (After Marshall.) 



A, auricle of heart. A Z>, dorsal aorta. B B, basi-branchial cartilage. B F y 

 fore-brain. B H, hind-brain. B M^ mid-brain. C, coelom or body-cavity. C', 

 pericardial cavity. C H, cerebral hemisphere. CB. rudimentary cerebellum. 

 CP, choroid plexus of fourth ventricle. CP\ choroid plexus of third ventricle. 

 7% pharynx. G, stomach. //, lung. 7, infundibulum. J, horny jaws, /f, lip. 

 L, liver. A", notochord. O, depression of floor of fore-brain from which the 

 optic nerves arise. OE, oesophagus. P, pituitary body. PN^ pineal body. S 1 , 

 central canal of spinal chord. 7", truncus arteriosus. V, ventricle. 



appears in each side of the mesenteron, at this 

 place, and by the meeting of these folds the 

 digestive tract is divided into a dorsal portion 



