The Development of the Cartilaginous Skull ete. in Necturus. 463 
v.12m. muscle of first and second va- VIII. auditory ganglion, 
gus arches, IX. glossopharyngeal ganglion, 
IT. optie nerve, X. vagus ganglion, 
ITI, oculomotor nerve, 1 (5), 2 (6) ete. postotic segments, the 
V. trigeminal ganglion, figure in parenthesis gives the num- 
VII. facial ganglion, ber of the head somite (v. WIJHE). 
Explanation of Figures. 
Plate XVI. 
1. Head of an embryo 11 mm long. 
la—1i. Horizontal sections through the head of an embryo 11 mm long. 
1b’. Left glossopharyngeal arch from fig. 1 4, enlarged. 
1g’. Right glossopharyngeal arch from fig. 1g, enlarged. 
12’. Left mandibular arch from fig. 1 ¢, enlarged. 
2. Model of the mesectodermic connective tissue in an embryo 10 mm long. 
3. Model of the wall of the branchial chamber in an embryo 10 mm long. 
4. Transverse section through the thyroid outgrowth. 
Plate XVII. 
. 5¢—5e. Horizontal sections through the head of an embryo 12!/, mm long. 
. 6a—6e. Horizontal sections through the head of an embryo 15 mm long. 
Plate XVIII. 
7. Model of the prochondral bars in Necturus, 15 mm long. 
. Ta—Te. ‘Transverse sections through the head of Necturus, 15 mm 
long. 
8. Procartilage of the mandibular arch. 
9. Model of the wall of the branchial chamber in Necturus 15 mm long. 
. 10. Sagittal section through the trabecular procartilage. 
. 11. Transverse section through the auditory vesicle, and the dorsal part 
of the mesothelium of the hyoid arch. 
. 12, Transverse section through the auditory vesicle, and the first pro- 
cartilage of the auditory capsule. 
. 13. Horizontal section showing the Anlage of the m. cerato-hyoideus internus. 
. 14. Diagram of the basal plate. 
. 15. 16. Model of the cartilaginous skull in Necturus 19 mm long. 
. 17. Transverse section through the auditory capsule. 
. 18. Sagittal section through the Anlage of the operculum auris. 
. 19. Transverse section through the mandibular arch and artery. 
. 20—24. Sagittal sections through the postotic segments. 
. 25. Diagram of the postotic segments. 
. 26. Sagittal section showing the mesothelium of the branchial arches. 
. 27. Copy of a horizontal section through the postotic somites in Siredon 
pisciformis, from fig. 12, plate V, SEWERTZOFF ’95. 
. 28. Transverse section through the Anlage of the auditory capsule in 
Necturus. 
. 29. Transverse section through the praeoccipital arch. 
. 30. Transverse section through the occipital arch. 
