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 



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.) 



^ . auricle of heart. A D^ dorsal aorta. ^^, basi-branchial cartilage. B F^ 

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

 pericardial cavity. C H^ cerebral hemisphere. ^B. rudimentary cerebellum. 

 C/', choroid plexus of fourth ventricle. CP\ choroid plexus of third ventricle, 

 /*, pharynx. (?, stomach. H^ lung. /, infundibulum. J^ horny jaws. K^ lip. 

 Z-, liver. iV, notochord. (9, depression of floor of fore-brain from which the 

 optic nerves arise. OE^ oesophagus. P^ pituitary body. PN^ pineal body. 5", 

 central canal of spinal chord. T^ 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 



