198 bulletin: museum of compaeative zoology. 



3. Ciliary Ganglion. The ciliary ganglion projects as a large mass of 

 cells from the lateral and dorsal sides of that portion of ,the oculomotor 

 nerve which lies between the fundament of the dorsal rectus muscle and 

 the combined fundaments of the ventral and anterior rectus muscles 

 (Plate 7, Fig. 26, gn. cil.). The communicating ramus from the oph- 

 thalmic branch of the trigeminus connects with its lateral face. A com- 

 parison of its ganglion cells with those found along the ophthalmic 

 branch shows, as in Stage IV, a marked difference both in the size of 

 nuclei and in the amount of distinctive cytoplasm. In Plate 3, Figure 

 10, the three upper ganglion cells, a, ft, y, are from the ophthalmic 

 branch, the three lower ones, 8, from the ciliary ganglion. Cell a, near 

 which are shown several future Schwann's-sheath cells applied to the 

 neuraxons, is taken from the nerve close to the Gasserian ganglion. 

 Cell ft is found at the base of the communicating branch running to the 

 ciliary ganglion, in the position indicated in Plate 7, Figure 25, by ft • 

 while cell y occurs distal to ft at the point indicated by y in the same 

 figure. The smaller size of the ciliary ganglion cells, 8, is apparent. 

 Both along the ophthalmic branch and within the ciliary ganglion, occa- 

 sional "accompanying" cells can be observed in the act of dividing. 

 One from the ophthalmic branch is shown at cl. comit.', one from the 

 ciliary ganglion at cl. comit." 



Ganglion cells of the ophthalmic type lying along the communicating 

 branch have been mentioned above. In one case ophthalmic ganglion 

 cells can be traced along the branch to the boundary of the ciliary gan- 

 glion, but none can be detected within it ; in another, there can be seen 

 within the boundaries of the ganglion near the entrance of the communi- 

 cating branch two cells, which can with certainty be assigned to the 

 ophthalmic class. It is apparent that there is not a large contribution 

 of cells from this source to the ciliary ganglion ; yet it seems probable, 

 in view of the evidence derived from Stage IV, that at least a few oph- 

 thalmic ganglion cells have from that time on been making their wav 

 into the ciliary ganglion. If this be so, the large invading cells must 

 soon become modified, through decrease in size, into cells closely resem- 

 bling those of the ciliary ganglion, which have arisen in situ, for careful 

 search through the entire ganglion at this stage fails to reveal more than 

 two cells of the ophthalmic type within its precincts, and these lie close 

 to the entering end of the communicating branch, and hence appear to 

 be new arrivals. 



4. Abducent Nerve. Except for some increase in size, the sixth nerve 

 has not changed its appearance since the last stage. It springs from its 



