409 



the right. The dorsal aortse are distinctly separate throughout their 

 course. The walls of the first arch are now complete and no trabe- 

 culse are present within its lumen. 



Fig. 2. Reconstruction of the Aortic arches in E.abbit embryo of 9th day (2nd 

 half). I, II, III aortic arches, x evagination on dorsal aorta. ^ about 50. 



Efmbryo of the tenth day. Fig. 3 shows the reconstruction 

 of the aortic arches on the left side of an embryo of the tenth day 

 of development. Remnants of the first pair of arches still persist in 

 the form of lacunse distributed along its course. Complete second and 

 third pairs are present, running in the hyoid and first branchial 

 pouches respectively. The two dorsal aortae are now united along a 



Fig. 3. Reconstruction of the Aortic arches in Rabbit embryo of the 10th day. 

 X about 35. 



