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 D, dorsal aorta. B B^ basi-branchial cartilage. B F, 

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

 pericardial ca%-ity. C H, cerebral hemisphere. CB, rudimentary cerebellum. 

 CP, choroid plexus of fourth ventricle. C/", choroid plexus of third ventricle. 

 F, pharynx. G, stomach. H, lung. /, infundibulum. ./, horny jaws. A", lip. 

 Z,, liver. N, notochord. O, depression of floor of fore-brain from which the 

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

 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 



