264 THE ORIGIN OF VERTEBRATES 
As far as the anatomist is concerned, the evidence is becoming 
clearer and clearer that the nucleus of the IIIrd nerve is a composite 
ganglion composed of a number of nuclei, each similar to that of the 
trochlearis, so that if the trochlearis nucleus is a segmental motor 
nucleus, then the oculomotor nucleus is a combined nucleus belong- 
ing to at least four segmental nerves, each of which has the same 
value as that of the trochlearis. 
The investigations of a number of anatomists, among whom may 
be mentioned Gudden, Ohersteiner, Edinger, Kélliker, Gehuchten, 
all lead directly to the conclusion that this oculomotor nucleus is 
composed of a number of separate nuclei, of which the most anterior 
as also the Edinger-Westphal nucleus contains small cells, while the 
others contain large cells. Thus Edinger divides the origin of the 
oculomotor nerve into a small-celled anterior part and a larger 
posterior part, of which the cells are larger and distinctly arranged 
in three groups—(1) dorsal, (2) ventral, and (3) median. Between 
the anterior and posterior groups lies the Edinger- Westphal nucleus, 
which is small-celled; naturally, the large-celled group is that which 
gives origin to the motor nerves of the eye-muscles, the small-celled 
being possibly concerned with the motor nerves of the pupillary and 
ciliary muscles. I may mention that Kélliker considers that the 
anterior lateral nucleus has nothing to do with the oculomotor nerve, 
but is a group of cells in which the fibres of the posterior longi- 
tudinal bundle and of the deep part of the posterior commissure 
terminate. 
These conclusions of Edinger are the outcome of work done in 
his laboratory by Perlia, who says that in new-born animals the 
nucleus of origin of the oculomotor nerve is made up of a number 
of groups quite distinct from each other, each group being of the 
same character as that of the trochlearis. He finds the same 
arrangement in various mammals and birds, Further, he finds that 
some of the fibres arise from the nucleus of the opposite side, thus 
crossing, aS in the trochlearis; these crossing fibres belong to the 
most posterior of the dorsal group of nuclei, ¢.¢. to the nerve to the 
inferior oblique muscle. 
The evidence, therefore, points to the conclusion that the oculo- 
motor nucleus is a multiple nucleus, each part of which gives origin 
to one of the nerves of one of the eye-muscles. 
Edinger says that such an array of clinical observations exists, 
