ANIMAL BIOLOGY, 



[Part I. 



three great arterial trunks are developed, and how a passage is 

 made from the fish condition to the frog condition through the 

 tadpole condition. Fig. 62, i., shows the four branchial arches 



a.ao. 



U, 



Fia. 62. DEVELOPMENT OF AORTIC ARCHES HEART (FROG). 



i. Fish stage, n. Tadpole stage, m. Frog stage, iv. Heart of frog dissected 

 so as to show the internal structure, all detail being omitted. 



In i., ii., in. ca. Carotid artery, d. ao. Dorsal aorta, h. Heart, liy. Hyoidean 

 artery. U. Lingual artery. 1. Lung. pu. Pulmonary artery. 1, 2, 3, 4. 

 Branchial arteries. 



In iv. ca. Carotid opening, p. c. Pulmo-cutaneous opening, p. v. Opening of 

 pulmonary vein. s. ao. Opening of systemic aorta, s. v. Opening of sinus 

 venosus. v. Cavity of ventricle. 



of the fish, represented here as continuous, the afferent and 

 efferent branchial vessels being, for the sake of simplicity, 

 merged into one (cp. Fig. 59). The dotted arch in front is the 

 hyoid arch, not found in the adult fish. Fig. 62, II., shows the 

 state of things in the tadpole. The hyoid arch is developed and 

 gives origin to a lingual artery, the dorsal connection with the 

 carotid part of the epibranchial being slender. The first 

 branchial arch is well developed, and gives rise to the carotid. 

 The second branchial arch is also well developed, and gives rise 

 to the systemic aorta. A slender dorsal connecting branch 

 represents this part of the epibranchial. The third branchial 



