PLATE 5 



EXPLANATION OF FIGURES 



25 From section No. 127, 7.5 mm. human embryo (No. 256, Harvard Embry- 

 ological Collection), showing the epibranchial placode II, and the fusion with it 

 of the lower end of the ninth cranial ganglion (petrosum). X 100. 



26 From section No. 125, of the same embryo, showing the parathyreoid III 

 in its first appearance and its relation to the third aortic arch. X 100. 



27 From section No. 134, of the same embryo, showing the epibranchial 

 placode III and its relation to the vagus nerve. X 100. 



28 From section No. 143, of the same embryo, showing epibranchial placode 

 IV and its relation to the vagus nerve and ganglion. X 100. 



29 Photograph of a section of a 8.3 mm. human embryo (No. 59 Cornell Uni- 

 versity Collection), showing the development of the parathyreoid III and its 

 position in relation to the third aortic arch. X 120. 



30 Photograph of a section in the same embryo on the same side, 11 sec- 

 tions (110/x) intervening, to show the developing parathyreoid IV and its position 

 in relation to the fourth aortic arch. X 120. 



396 



