DEVELOPMENT OF THE BRAIN AND GANGLIA. • 61 



to the lower vertebrates, can lead to no satisfactory results. The task of 

 sufficiently describing the cranial nerves is to be accomplished in no other 

 way than the following: (1) in gradually becoming acquainted with all of 

 the separate nerves that correspond to a single segment of the head, and (3) 

 in determining how these have been combined into larger trunks. 



So far as we know at present, the simplest relations exist in the embryos 

 of Cyclostomii. It is especially to Kupfier that we are indebted for the 

 beginning of a somewhat clearer vision here. (See Figs. 26h and 36c.) 



Note in the Ammoccetes of only four millimeters that the chain of 

 epibranchial ganglia is connected dorsally with the five much larger dorso- 

 lateral ganglia. The most anterior one of the latter is the Ggl. ophthal- 

 micum. From this most of the fibers which constitute the ophthalmic 

 branch of the Trigeminus later develop. Posterior to this, and connected 

 with the central system through two roots, lies the Ggl. maxillo-mandibulare. 

 It will later be fused with the Ggl. ophthalmicum to form the Ganglion Gas- 

 seri and will give off the second and third branches of the Trigeminus. But 

 in the meantime, fibers and ganglion-cells from the anterior epibranchial 

 ganglia have become associated with the elements already enumerated. So 

 the N. trigeminus is to be looked upon as already a most complicated struct- 

 ure, containing elements of most varied origin. Anterior to the otocyst 

 lies the great ganglion of the Facialis, connected with the sixth and seventh 

 epibranchial ganglia. When the animal becomes larger one recognizes that 

 this ganglion is only an appendage of the great composite root of the 

 Facialis; that in the composition of this nerve not only do fibers from the 

 ganglion in question participate, but also numerous structures which arise 

 from the now gradually disappearing epibranchial ganglia. Just posterior 

 to the ganglion of the Facialis the previously continuous trunk of the epi- 

 branchial ganglia comes to an end (see Fig. 36c and compare Fig. 36&). 

 Parts of this trunk are received anteriorly into a Ramus luccalis, and pos- 

 teriorly into peripheral facial branches. 



Here is an example of that which the author stated above regarding 

 the value or significance of single nerves. The apparently single facial 

 nerve contains elements of the most manifold origin and significance. 



Posterior to the otocyst lie the Ggl. Glosso-pharyngei and the Ggl. Vagi; 

 both intimately connected with the corresponding epibranchial ganglia. 

 Later, when the epibranchial chain is broken, it remains intact posterior 

 to the ganglion of the Vagus, where it appears like a nerve-trunk passing off 

 from that ganglion and containing ganglionic nodes. It is the N. pneumo- 

 gastricus, the Vagus, and it innervates the gills, heart, and other viscera. 



