ioS 



PL ATT. 



DESCRIPTION OF PLATE IV. 



Fig. i. Embryo of 6 mm. The four anterior head cavities are shaded, and the 

 anterior cranial nerves outlined. 



Fig. 2. Anterior head cavities from an embryo of 12 mm. 



Anterior head cavities from an embryo of 16 mm. 



Eye-muscles from an embryo of 22 mm. 



Eye-muscles from an embryo of 27 mm. 



Eye-muscles from an embryo of 35 mm. 



Eye-muscles from an embryo of 55 mm. 



Anterior part of the dorsal aorta in an embryo with one complete aortic 



Fig. 3 

 Fig. 4 

 Fig. 5 

 Fig. 6, 

 Fig. 7 

 Fig. 8 

 arch. 

 Fig. 9 



Anterior part of the dorsal aorta in an embryo with two complete aortic 



arches. 



Fig. 10. Anterior part of the dorsal aorta and of the cardinal veins in an embryo 

 with six complete aortic arches. 



Fig. 11. The anastomosis of mandibular artery, hyoid vein, and first branchial 

 vein. The figure also shows the five vein commissures of the first branchial arch. 



