46 Dixon—On the Development of the Branches of the Fifth Cranial Nerve in Man. 
present.” ‘In short, the development of nerves is not an outgrowth of cell 
processes from certain central cells, but is a differentiation of a substance which is 
already in position, and this differentiation seems to take place from the medullary 
walls outwards to the periphery, both in the anterior and posterior roots, and to 
precede, or to proceed pari passu with, the development of the other tissues.” 
Notwithstanding the assertions of Sedgwick to the contrary, the axis-cylinders 
have been proved to be processes of ganglionic cells, and not only to arise as such 
in the embryo, but to exist as such in the adult. His statement (p. 94) that ‘“‘ The 
neuroblasts of His, and other authors, are nuclei lying in a substance which, after 
death caused by ordinary re-agents, has usually a fibrous structure,” proves 
nothing, as long as nerve cells and their processes can be made out in perfectly 
fresh tissues, without the use of re-agents. Further, it seems scarcely expedient 
to remove the idea and word “cell” from anatomical description until Sedgwick 
can prove that animals which possess white blood corpuscles do not possess cells, 
in the general acceptation of the term, and therefore are not multicellular. The 
observations of physiologists and pathologists are also in favour of the cellular 
conception of the neuroblasts. 
One important observation made by Sedgwick must here be noticed: writing 
of the third nerve, Sedgwick says that it, unlike the Gasserian ganglion, the 
mandibular branch of the fifth, the ramus profundus, and the ciliary (mesocephalic) 
ganglion does not ‘“‘crystallise” out of the nerve crest, but ‘first makes its 
appearance as a forward projection from the ciliary (mesocephalic of Beard) 
ganglion. This forward projection extends itself, until it reaches the base of the 
midbrain.” ‘The third nerve, therefore, presents this interesting and remarkable 
peculiarity in Scyllium and Acanthias: it grows or is differentiated from the 
ciliary ganglion to the floor of the mid-brain, and not in the opposite direction, as 
has hitherto been supposed.” 
With regard to this observation by Sedgwick, we have, I believe, a somewhat 
similar case in the development of the fourth nerve in Acanthias as described by 
Miss Platt. According to this author the fourth nerve is partly, at all events, 
developed as a cellular growth, or as Sedgwick would probably call it, ‘a cord of 
nuclei with rather dense pale substance,” which grows from the ganglion of the 
fourth nerve towards the brain. According to Miss Platt, however, the fibrous 
fourth nerve, 7c. the axis cylinders, grow out from the brain itself, and not in the 
opposite direction. It seems then to me that in the case of the third nerve also, 
although a cord of nuclei may grow from the ganglion of the ophthalmicus 
profundus to the mid-brain in the forms studied by Sedgwick, that yet the fibres of 
the third may grow in the opposite direction through this nuclear cord which 
would then represent the ‘‘nervenfiirendes” tissue of Goronowitsch. In 
mammals certainly the fibrous third nerve is developed from the brain outwards, 
