Drxon——On the Development of the Branches of the Fifth Cranial Nerve in Man. 47 
and an examination of the specimens make it impossible to believe that the fibres 
in the early stage are not processes of cells in the brain. 
Miss Platt has also traced the origin of the ‘cellular third nerve” as an out- 
growth from the ciliary (or profundus ganglion). On the other hand, Gorono- 
witsch says distinctly that the cellular cord which at first occupies the position of 
the future third nerve is developed independently of the nerve crest (ganglion- 
leiste) from the mesenchyme, both in the chick and in bony fish. This cellular 
cord of Goronowitsch will afterwards be traversed by the axis cylinder processes 
of the true third nerve (p. 233). 
It does not seem that Sedgwick has proved that the fibrous third nerve, #.c., 
the functional third of the adult is developed in Elasmobranchs in a different 
manner from other motor nerves. The observations of Dohrn, on the other hand, 
Ficure 2. 
Outlines of portions of two consecutive horizontal sections through the head of a rat embryo of 16 days. ‘The sections lie 
near the region of origin of the fourth nerve. In the first, the fibrous fourth nerve is seen just as it enters the ‘‘ ganglion,” 
and in the second, the position of the ganglion is shown, cut at right angles to its long axis. A. artery. H. cerebral hemi- 
sphere. Isth. isthmus. J. tributaries of jugular vein. iii. third nerve. iy. fourth nerve. iv’. ganglion of fourth nerve. 
8rd, third verticle. 
show that the fibres of the nerve in Elasmobranchs are developed from the brain 
towards the periphery, and, therefore, in accordance with other motor nerves. 
The description of the fourth nerve given by Dohrn seems to throw light on the 
observation of Sedgwick. The cells of the ganglia of the fourth nerve are de- 
scribed by Dohrn as derived from the trigeminal complex, but yet the fibres 
of the nerve are formed from processes of the brain cells growing outwards. 
The fibrous third nerve, like the fibrous fourth, will grow out from the brain 
as it has been described by so many authors. I may say that in the rat embryo 
