Drxon—On the Development of the Branches of the Fifth Cranial Nerve in Man. 28 
enlarged, results. Sometimes it is only necessary to draw every second section, 
and in these cases glass plates twice as thick were employed. In places where 
nerves cross, or where they are closely applied one to another, it is necessary 
to draw every section. By the use of different coloured inks for the different 
nerves and vessels, the tracing of the relative positions and connections of the 
various structures in the model is simplified. It is advisable to gum small 
pieces of paper on the glass plates near the corners, so as to prevent the 
varnish being rubbed, or scratched; where this occurs the model becomes 
opaque. Further, in drawing the outline of the larger structures, such as the 
brain, experience showed that it was well to use only dotted lines. When thick 
lines are multiplied in the model, the whole becomes too dark, and the nerves are 
not easily seen or traced as they pass behind these more solid structures. Models 
constructed in this way have the great advantage that they can be cut in section 
at any point by simply separating the plates, or indeed, if desired, any individual 
section can be studied. Further, if a mistake is found at any place, the faulty 
plate or plates can be removed, washed under running water, and re-drawn.* 
When the model consists of a very large number of plates, 100—200, it cannot 
be viewed as a whole even by a bright transmitted light ; but it is very useful to 
divide it up into a number of parts of from 10—20 plates, each of which we may 
take to represent a very thick section through the head multiplied 25 or 50 
diameters. The drawings accompanying this paper are made from such groups of 
plates, and the actual thickness of the sections which they represent are given in 
each case. 
Ophthalmic Division of the Fifth Cranial Nerve. 
Emepryo Br;.—(4 weeks, 6°9 mm.). Figure 5, Plate I. 
In this embryo the ophthalmic nerve is represented by a relatively thick 
trunk, taking origin from the highest point of the Gasserian ganglion. 
This trunk is short, being only 0-4 mm. in length, and its direction is almost 
directly upwards behind the eyeball. Towards its termination, however, the 
nerve turns slightly inwards, the turning inwards corresponding to the narrowing 
of the head at this level. The nerve-trunk gives off no branches. Among the 
tibres of the nerve a number of nuclei are present, but no aggregation of these 
into an isolated ganglion was found. These nuclei are most plentiful near the 
origin of the nerve from the Gasserian ganglion. 
As a rule it was noted both in man and in the rat that nuclei are most plentiful 
among the fibres of a nerve near its origin from the ganglion from which it grows 
out, and further, they are more numerous in the early than in the later stages. 
* Dr. Oskar Israel in his Practicum of Pathological Histology, Berlin, 1893, p. 96, attributes to Klebs a 
method of reconstruction similar to the one here described. I have not been able to see Klebs’s original 
description. 
