520 H. W. NORRIS AND SALLY P. HUGHES 



of the basal bone and farther anteriorly at the lateral border of 

 the dorsal trabecular cartilage bar (figs. 22-20, 16). It con- 

 tinues unbranched as far as the level of the choana. There a 

 branch of the ramus ophthalmicus profundus joins it in such a 

 way as to render it difficult to follow the facialis fibers with cer- 

 tainty. Along with twigs of the fifth nerve, they are soon dis- 

 tributed to the skin of the dorsal lateral part of the head in a 

 region slightly anterior to the position of the eye (figs. 10-8, 

 op.l -\- OS). The significance of this nerve will be discussed 

 later in connection with the facialis. 



5. The ravius ophthalmicus profundus V 



As the ramus ophthalmicus profundus passes out of the oph- 

 thalmic ganglion, the abducens nerve lies at its ventral border 

 and continues with it anteriorly, but gradually separating from 

 it, until the retractor muscle of the tentacle is reached (figs. 

 22-20, op., VI). The ramus ophthalmicus profundus at first runs 

 close to the lateral border of the orbitosphenoid region of the 

 basal bone (figs. 22, 21), then, farther anteriorly, in the same re- 

 lation to the membrane which closes the great intertrabecular 

 foramen (figs. 20, 16), and to the bony trabecular wall. As it 

 passes anteriorly it gradually rises dorsally, giving off no branches 

 until the level of the choana is reached. Here a large nerve 

 (op.l) is given off, a branch of which comes into close relation- 

 ship with the nerve derived from the facialis (os.), as described 

 in the preceding section (figs. 10-8). Soon after giving off the 

 larger nerve the ramus ophthalmicus profundus enters a canal 

 in the dorsal part of the ethmoid bone (fig. 10) and continues in 

 it until the level of the anterior end of the olfactory lobe is 

 reached. There the nerve continues in the dorsal part of the 

 nasal chamber on the ventral border of a lateral wing-like exten- 

 sion of the ethmoid (fig. 8, op.2), and farther anteriorly along 

 the medial ventral border of the dorsal portion of the nasopre- 

 maxilla (figs. 4-2), and finally in a canal in the same bone to its 

 distribution to the skin of the tip of the snout (fig. 1). 



On its course from the ganglion to its final distribution the 

 ramus gives off comparatively few branches. The first branch. 



