DESCRIPTTON OF PLATE XXYll—conlinned. 



Figs. 1 and 2. — Transverse sections tlirough the hind brain of a Sc^llhcm 

 embryo, intermediate between stages i and K. X 90. 



Fig. 1, showing dorsal (primary) and ventral (secondary) roots of 

 fifth nerve ; also the second or mandibular head cavity. 



Fig. 2, showing origin of dorsal (primary) roots of seventh nerve 

 from neural crest; also the third or byoidean head cavity. 



Figs. 3 and 4. — Transverse sections through the hind brain of an embryo 

 of stage K. X 90. 



Fig. 4, showing the fifth nerve, arising by its ventral or secondary 

 root alone. 



Fig. 3, showing the dorsal and ventral roots of the seventh nerve. 



Figs. 5 to 7. — Transverse sections through the hind brain of an embryo of 

 stage N. X 20. 



Fig. 5, showing the ventral roots of the fifth nerves, the ophthalmic 

 branches of the seventh nerves, and the terminations of the maxillary 

 branch of the fil'tli and the buccal branch of the seventh nerve ; also 

 the first head cavity. 



Fig. 6, showing the dorsal and ventral roots of the seventh nerve, 

 the buccal branch of the seventh and maxillary branch of the fit'tii, 

 and the connection between these two nerves ; also the second head 

 cavity. 



Fig. 7 shows on the left side the ventral root of the seventh nerve, the 

 termination of the sixth nerve in the rectus externus, the mandibular 

 branch of the fifth nerve, the second head cavity, and the termination 

 of the palatine branch of the seventh nerve. On the right side, 

 M'hich represents a more posterior section, are shown the origin of 

 the sixth nerve, the auditory nerve and vesicle, and the palatine 

 branch of the seventh nerve, with the second head cavity. 



Figs. 8 and 9. — Transverse sections through the hind brain of an embryo 

 of stage 0. X 17. 



Fig. 8, showing the ventral root of the fifth nerve ; also the optic 

 nerves and infundibulum. 



Fig. 9, on left side, shows the dorsal and ventral roots of the 

 seventh nerve, and the terminal branches of the buccal and maxillary 

 nerves ; on the right side the auditory vesicle, the seventh nerve with 

 its hyoideau branch, and the termination of the palatine nerve. 



Fig. 10. — Longitudinal and vertical section through the head of an embryo 

 of stage L. The outline is from one section, while the details have 

 been filled in from several consecutive sections in order to show the 

 roots of the fifth and seventh nerves, the relations of the third, fifth, 

 and seventh nerves to the head cavities, and the connections of these 

 three nerves with one another. The figure also shows the glossopha- 

 ryngeal nerve with its ramus clorscdis, and its hyoidean branch. X 25, 



Figs. 11 and 12.— Diagrammatic longitudinal and vertical sections through 

 the head of an embryo of stage N ; as in the preceding figure, the 

 outline was drawn from one section, and the details froni other sec. 

 tious of the same embryo. 



The two figures together show the roots and all the branches, with 

 their terminal distribution, of the fifth and seventh nerves, the con- 



