48 Dixon—On the Development of the Branches of the Fifth Cranial Nerve in Man. 
the “ ganglion” of the fourth nerve is a most conspicuous object, yet the fibrous 
fourth nerve is not developed from it towards the brain, but in the opposite 
direction, as in Elasmobranchs (Dohrn and Miss Platt). This “ ganglion” of the 
fourth nerve is easily demonstrated in rat embryos after the thirteenth day. The 
nerve at its origin from the brain is fibrous, and also near its termination, where 
it is in relation to the frontal nerve. In the intermediate part of its course, on the 
other hand, the fourth nerve is represented by a relatively thick dense cellular 
cord. The cells of this cord have very distinct nuclei, and although among them 
there are some fibres, these latter are not nearly so conspicuous as those 
which form the fourth nerve above the ‘‘ ganglion.” The three accompanying 
drawings (figs. 2 and 3) illustrate the “ganglion” of the fourth nerve in the rat 
embryo. The “ganglion” appears first to have been described by Hofimann* 
in reptiles; since then it has been described by Dohrn and Miss Platt? for 
Elasmobranchs. Dohrnt describes it as a cut off portion of the Trigeminal 
complex. In neither Elasmobranchs nor in the rat does it give rise to the fibrous 
fourth nerve, which grows out from the brain itself. I would venture to suggest 
that in this “‘ ganglion” of the fourth nerve we have a similar structure to the 
cellular third nerve which Sedgwick describes as being developed from the 
anterior part (nasal) of the Gasserian ganglion towards the brain. In both cases 
we have a process of the Gasserian ganglion growing towards the brain, and in 
the case of the third nerve, just as in that of the fourth, all observers describe the 
jibres as growing out from the brain. 
It must be noted that Dohrn§ contrasts sharply the ganglia of the third and 
fourth nerves, in Elasmobranchs, and considers the third nerve and its ganglion, to 
be developed in quite a different manner. Miss Platt’s description agrees more 
closely with that of Sedgwick. On the other hand, it is just possible, that 
Sedgwick’s third nerve may represent Kwart’s|| ciliary ganglion, which is 
developed as a process of the ganglion of the ramus profundus. 
When now we leave the question of the origin of the ciliary ganglion, and 
inquire what is the nature of the ganglion in the adult, we have at last certain 
information. 
In 1881 Retzius, from microscopic examinations of the ciliary ganglion, came 
to the conclusion that it was sympathetic in nature. Onodi, Hoffmann, Beard, 
and a number of others, arrived at the same conclusion from observations on its 
* «Uber du Metamerie des Nachhirns und Hinterhirns, und ihre Bezichung zu den segmentalen Kopf- 
nerven bei Reptilienembryonen,” Zool. Anzeiger, 1889, p. 337. 
+ Journal of Morphology, 1891, vol. v., p. 79. 
{ Mitt. a. d. Zool. Station zu Neapel, 1890, Bd. x., p. 11. 
§ Mitt. a. d. Zool. Station zu Neapel, Bd. x., 1891, p. 11. 
|| On the development of the ciliary or Motor Oculi Ganglion. Proceedings of the Royal Society, vol. 
47, 1889, p. 287. 
