Embryonic history of the aortic arches in mammals. 433 



Fig. 9. Surface view of the left side of a rabbit embryo of 11 Va 

 days development. 12^/^ : 1. 



Fig. 11. Surface view of the left side of a rabbit embryo of 12^2 

 days development. 12^2 • 1- 



Fig. 13. Surface view of the right side of a pig embryo of tbe 

 20th day (early). 10 : 1. 



Fig. 15. Surface view of left side of a pig embryo of the 20th day 

 (No. 2). 10: 1. 



Fig. 17. Surface view of the right side of a pig embryo of the 

 20th day (No. 3). 10 : 1. 



Fig. 19. Surface view of the left side of a pig embryo of the 20th 

 day (No. 4). 10 : 1. 



Fig. 21. Surface view of the right side of a pig embryo near the 

 close of the 20th day (No. 5). 10: 1. 



Fig. 23. Surface view of the left side of a pig embryo of 21 days 

 development. 6^/3 : 1. 



Fig. 25. Surface view of the right side of a pig embryo of the 

 22nd day (probably). TV^ : 1. 



Fig. 27. Surface view of the right side of a pig embryo of a later 

 stage (23rd day?). 8:1. 



Plate 23. 



Fig. 2. Reconstruction of the aortic arches in a rabbit embryo of 

 the first half of the ninth day of development. 87 : 1. Surface view 

 of the same is shown in Fig. 1 . //, //' rudiments of the second aortic arch. 



Fig. 4. Reconstruction of the aortic arches in a rabbit embryo of 

 the second half of the ninth day of development. 50 : 1. Surface view 

 of the same is shown in Fig. 3, y an isolated sinus, x apparent dorsal 

 bud of the fourth arch. 



Fig. 6. Reconstruction of the aortic arches in a rabbit embryo of 

 ten days development. 36 ^/^ : 1. Surface view of the same is shown in 

 Fig. 5. 1 remnants of the degenerating first aortic arch, x an asymmetrical 

 evagination from the third arch, present only on the left side. 



Fig. 8. Reconstruction of the aortic arches in a rabbit embryo of 

 eleven days development. 36 ^g : 1. Surface view of the same is shown 

 in Fig. 7. //, // remnants of the degenerating second aortic arch. / 

 ventral bud of sixth arch, x and y possible rudiments of a fifth aortic arch. 



Fig. 10. Reconstruction of the aortic arches in a rabbit embryo of 

 eleven and one-half days development. 49 : 1 , Surface view of the same 

 is shown in Fig. 9. a sinus in front of ventral end of second arch. 

 F possible rudiments of fifth arch. 



Fig. 12. Reconstruction of the aortic arches in a rabbit embryo of 

 twelve and one-half days development. 22^2 • 1- Surface view of the 

 same is shown in Fig. 11. //, 11 probable remnants of the second arch. 



