Dixon—On the Development of the Branches of the Fifth Cranial Nerve in Man. 45 
the “‘ ganglienleiste” becomes changed into mesenchyme, before the ganglia of 
the fifth nerve appear. ‘The ciliary ganglion is formed by cells migrating into 
the course of the third nerve from the brain.* 
Sedewick,t in his attack on the cellular theory of development, describes for 
Elasmobranchs, conditions practically similar to those given by Goronowitsch for 
the chick. 
He states-—‘‘ The nerve crest does not, as was first stated by Balfour, and 
afterwards by all authors, on the development of nerves, give rise exclusively, or 
even principally, to nerves and ganglia. It gives rise to nuclei, which spread out 
in and add to the mesoblastie reticulum, which, at all times, 7.e., from the very 
beginning, exists between the layers, and to nuclei, which become the nuclei of 
rudiments of the nerve ganglia.” 
We must now inquire what, according to these two authors, is the origin of the 
ganglia and the nerves connected with them. According to Goronowitsch, before 
true nerves—axis-cylinders processes—or ganglia appear, in the case of the fifth 
nerve two processes of cells become differentiated from the mesenchyme round 
about. These two processes meet together in a common cellular mass, and are not 
true nerves, but simply cellular cords, differentiated from the rest of the 
mesoblast. From them the sheaths of the true nerves, which appear later, will be 
developed; into one of the cords the neuroblast fibres of the ophthalmic nerve will 
later on grow out, into the other, those of the inferior maxillary nerve. No cord 
of cells is at first present to represent the superior maxillary nerve. The cells of 
the ganglia arise far away from the medullary canal, in the region of the 
‘* Froriepschen anlagen.” 
Sedgwick, for Elasmobranchs, describes certain parts of the neural crest 
(ganglienleiste) as remaining “‘unaltered and characterised by a greater density of 
nuclei,” while the greater part of it breaks up into a reticulum called mesoblast. 
These unaltered tracts ‘‘ mark the course of the future nerves and the sites of the 
future ganglia.” 
“The Gasserian ganglion, the ophthalmicus profundus, the mandibular branch 
of the fifth, and the ciliary ganglion (mesocephalic of Beard) thus emerge from 
the remains of the nerve crest, are so to speak crystallised out of it” (p. 96). 
Like Goronowitsch, he compares the neural crest to the primitive streak—a centre 
for the growth of nuclei. Unlike Goronowitsch, he does not believe in the 
neuroblasts of His, for ‘“‘the nerves are laid down before any nerve cells are 
* « Untersuchungen tiber die Entwicklung der sog. ‘ Ganglienleiste’ im Kopfe der Vogelembryonen,” 
Morphologisches Jahrbuch, Bd. 20, 1898. 
} ‘‘On the Inadequacy of the Cellular Theory of Development, and on the Early Development of 
Nerves, particularly of the Third Nerve, and of the Sympathetic in Elasmobranchii,” Quarterly Journal 
of Microscopical Science, 1894, p. 87. 
H? 
