122 PROF. MARSHALL AND MR. SPENCER. 



second head cavity, and the termination of the palatine 

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

 represents a more posterior section, are shown the origin 

 of the sixth nerve, the auditory nerve and vesicle, the 

 palatine branch of the seventh nerve, and the second 

 head cavity. 



Figs. 8 & 9. Transverse sections through the hind-brain of an embryo 

 of stage o. x 17. 



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

 optic nerves and infundibulum. 



Fig. 9, on the 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 audi- 

 tory vesicle, the seventh nerve with its hyoidean 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 consecu- 

 tive 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 glossopharyngeal nerve with its ramus dorsalis, 

 and its hyoidean branch, x 25. 



Figs. 11 & 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 from other sections 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 connections of these nerves .with one another 

 and with the third nerve, the principal branches of the 

 third nerve, and the course and distribution of the fourth 

 and ninth nerves, at stage n. No single section could 

 show all or even the greater number of the parts repre- 

 sented in either of these figures, as they lie at very 

 different levels, x 25. 



