PLATE 2 



EXPLANATION OF FIGURES 



3 Cat embryo, 12 mm. Sternal bands are far apart. No presternum pres- 

 ent at this stage. The first three pairs of ribs fail to reach the sternal bands. 

 From the Princeton Embryological Collection, series no. 401. Graphic recon- 

 struction. 



4 Cat embryo, 14 mm. Sternal bands nearer to each other. Presternum 

 has arisen and connects the anterior ends of sternal bands. All ribs reach the 

 sternum. From the Princeton Embryological Collection, no. 37. Graphic 

 reconstruction. 



PSt, presternum R,* fourth rib 



R\ first rib R, 7 seventh rib 



R 3 , third rib StB, sternal bands 



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