PLATE 3 



EXPLANATION' OF FIGURES 



7 Trans\erse section of a 6 mm. toad embryo through tlie sinistro-ventral 

 region of the head. Series 54, slide 1, row 4, section S. X 1100. 



REFERENCES 



/., sinus anlagen 



j.s., left external jugular vein 



8 and 9 Transverse sections of another 6 mm. toad embryo through the dextro- 

 ventral region of the head. Series 53, slide 1, row 5, section 13, and row 6, section 

 4. • X 1100. Eight sections intervene between these two levels. 



REFERENCES 



/.I. /.2, /.3, sinus anlagen 



j.d., right external jugular vein 



t.j., wall of a tributary cut tangentially 



188 



