190 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



The rule played by the ophthalmic branch of the trigeminus in the 

 development of the ciliary ganglion will be considered under the follow- 

 ing heading. 



3. Ciliary Ganglion. As has been stated, the ciliary ganglion lies 

 mainly on the lateral side of the third nerve near its distal extremity. 

 Its form in transverse section, and its general relation to the ophthalmic 

 branch of the fifth nerve and to the eyeball, are shown in a diagram- 

 matic way, for the right side of the head, in Plate 4, Figure 1 3. The 

 striated portion represents the fibrils of the oculomotor, while the 

 ciliary ganglion is indicated by the evenly shaded part. The ganglion 

 contains, now for the first time, cells so far advanced in differentiation 

 that they can be declared without hesitation to be young ganglion cells 

 (Plate 5, Fig. 16, E). Interspersed among them are a few cells (E, cl. 1 , 

 cl.") exactly like the "accompanying" cells of the nerve fibrils. The 

 ganglion is no longer, as in the preceding stage, the scene of active 

 cell division. A few of the young ganglion cells lie along the median 

 border of the nerve opposite the laterally placed body of the ganglion. 

 Figure 13 (Plate 4) also shows the ophthalmic branch of the trigem- 

 inus (rm. opth. trig.) cut transversely. A small offshoot is indicated, 

 running from this nerve in the direction of the ciliary ganglion, which, 

 however, it fails to reach. The fibrils of this branch become lost in the 

 mesenchyme, so that it is not possible to trace them all the way to the 

 ganglion, although, on the opposite side of the head, where development 

 is a little more advanced, this can be done. I have also indicated 

 in the figure all the ganglion cells to be found along that segment of 

 the ophthalmic branch of the trigeminus which lies opposite the ciliary 

 ganglion as well as all the ganglion cells that have become detached 

 from the ophthalmic branch at this level. The number and positions 

 of these cells were ascertained by studying the series of consecutive 

 sections extending from the anterior to the posterior face of the ciliary 

 ganglion, and recording the ganglion cells observed by projecting them 

 on the plane of the diagrammatic section represented by Figure 13. 



A comparison of the ganglion cells of the ophthalmic branch of the 

 trigeminus with those of the ciliary ganglion will prove instructive. In 

 Figure 16 at A are shown two ganglion cells (a, /3), taken from the 

 ophthalmic branch, their positions in that nerve being indicated by 

 the same letters in Figure 13. The ganglion cells of the group E were 

 taken at random from the ciliary ganglion. They exhibit the features 

 characteristic of young ganglion cells, resembling those of the ophthalmic 

 branch in the possession of deeply staining granular cytoplasm, accumu- 



