332 Journal of Comparative Neurology. 



eighth gill pouches, between the rr. post- and prietrematici, show the 

 locations of the later appearing spiracula externa. 



J^iff. 9. Ii, hind brain; a, aorta; «/, muscle; I', principal ganglion 

 of vagus; 7, seventh epibranchial ganglion; g-, rudiment of a gang, prse- 

 trematicum, with which the r. preetrematicus is connected. Inwards 

 from it twigs of the r. posttrematicus. s, a sjmpathic ganglion; iid, 

 neurodermis. ^Y^- 



J^ig^- 10. h, mid brain; A, eje; cli, chorda; A', prtechordal head 

 cavity, connected by means of the hollow connecting cord with that of 

 the other side; w, stomodseum; vs, foremost ventral spinal nerve; ds, 

 foremost dorsal spinal nerve; nd, neurodermis. ^\^ . 



Fig. 11. Dorsal cranial nerves of adult Ammocoutes, i.e., Petro- 

 myzon, semi-diagrammatic. The ganglia, especially those caudad, are 

 somewhat separated, so as not to overlap in the figure. A, eye; iV, nose; 

 O, cartilaginous auditory capsule; A', foremost gill cleft; /, first, //, 

 second principal ganglion of trigeminus; ///, principal ganglion of 

 facialis; /V, principal ganglion of glosso-pharyngeus; I', principal 

 ganglion of vagus; 1, first, 7, seventh epibranchial ganglion (comp. 

 Fig. 8); ;-«, ramus anterior; ;-/, ramus posterior; rr, ramus recurrens 

 of the facialis. 



Note. — The fractions representing the amplification of the figures are those accom- 

 panying the original. All the figures have been somewhat reduced during reproduction. 

 —Ed. 



