DEVELOPMENT OF THE BLOOD VESSELS IN THE FROG. 267 



tion between the truncus arteriosus and the aorta. On 

 the right side the section passes through the first branchial 

 gill pouch : ( x 45). 



Tig. 6. 5 mm. tadpole. A diagrammatic figure of the anterior part 

 of the tadpole, seen from the right side, and showing the 

 condition of the heart and blood vessels : ( x 45). 



Fig. 7. 6|- mm. tadpole. A diagrammatic figure of the anterior part 

 of the tadpole, seen from the right side, and showing the 

 condition of the heart and blood vessels : ( x 45). 



Fig. 8. Qh mm. tadpole. A diagrammatic transverse section through 

 the head, just behind the auditory vesicles, and seen 

 from behind. The section passes through the first 

 branchial arch on each side. On the right side, both the 

 afferent and efferent vessels of this arch are shown ; on 

 the left side, the greater part of the afferent vessel has 

 been removed in order to expose the efferent vessel more 

 thoroughly: (X 45). 



Fig. 9. 6£ mm. tadpole. A diagrammatic horizontal section through 

 the anterior part of the tadpole. The general level of 

 the section is that of the dorsal part of the pharynx just 

 below its roof. On the right side, the section is taken at 

 a level slightly ventral to that shown on the left side. 

 On the left side, the whole course of the dorsal aorta 

 and its branches are shown, together with the external 

 gill of the second branchial arch, and the three nephro- 

 stomes of the head kidney. On the right side, the gill 

 pouches are shown, together with the vessels of the several 

 arches : (x 45). 



Fig. 10. 6| mm. tadpole. A diagrammatic horizontal section through 

 the anterior part of the tadpole, taken at a level ventral 

 to that of Fig. 9, and showing the heart and afferent 

 branchial vessels as seen from above. On the right side 

 the section is taken at a level slightly ventral to that 

 shown on the left side : (x 45). 



Fig. 11.0 mm. tadpole. A diagrammatic figure of the anterior part 

 of the tadpole, seen from the right side, and showing the 

 condition of the heart and blood vessels : (x 45). 



