BULL. U. S. B. F. 1912. 



PLATE LVIII. 



II 



11 



FIG. 5. Redrawn from Maurer, 1886. Thyroid of n trout 20 cm. long; shown in its relation to the branchial arteries, 

 seen from the ventral side. 



FIG. 6. Redrawn from Maurer. Median section to show distribution of thyroid about the ventral aorta in a trout 2.5 

 cm. long. 



FIG. 7. Redrawn from Maurer. Cross section of the head of a trout embryo of 30 days, showing earliest evagination 

 of pharyngeal epithelium to form the thyroid. 



FIG. 8. Redrawn from Maurer. Median section through head of trout embryo of 35 days. Primary thyroid vesicle 

 (/) still attached to parent epithelium by pedicle. 



FIG. 9. Redrawn from Maurer. Cross section of a trout embryo of 35 days. Primary thyroid vesicle (/) separated from 

 parent epithelium. 



FIG. 10. Redrawn from Maurer. Median section through head of trout embryo of 41 days. Compared witli figure 8, it 

 shows that the elongated primary thyroid vesicle (/) has moved backward and now lies ventral to the aorta. 



FIG. 11. Drawing showing gross appearance of jugular pit from below. 



