PLATE 4 



EXPLANATION OF FIGURES 



10 Transverse section of a 7 mm. toad embryo through the ventral region of 

 the head. Series 52, slide 1, row 4, section 5. X 300. 



11 A small area near the lower left corner of the same section (fig. 10). 

 X 1100. 



REFERENCES 



j.d., j.s., right and left external jugular /., I., sinus anlagen 

 veins m.c, mouth cavitv 



190 



