168 
Proceedings of Royal Society of Edinburgh. [sess. 
On the Segmentation of the Nucleus of the Third Cranial 
Nerve. By Dr Alexander Bruce. (With Two Plates.) 
The circumstance that the oculomotor or third cranial nerve 
supplies no fewer than seven muscles of the eye, two of them 
intrinsic and five extrinsic, and the fact that these muscles may be 
paralysed either singly or in groups as the result of central 
lesions, naturally suggest that each muscle is represented in the 
nucleus by a separate group of nerve cells. Hitherto, however, 
the anatomical text-books have been content with figuring the 
nucleus as a small indefinite group of cells lying in the anterior 
portion of the grey matter surrounding the aqueduct of Sylvius. 
The well-known experiments of Hensen and Yolckers ( Graefe's 
Archiv , Bd. xxiv., 1878, p. 1) would appear to have been the first 
attempt to investigate the question. They exposed the nucleus in 
the dog, and by stimulating its various portions with electricity, they 
came to the conclusion that the centres of the various muscles 
were arranged from above downwards in the following order : — 
(1) Tensor choroidese (accommodation). 
(2) Sphincter iridis. 
(3) Rectus internus. 
(4) Rectus superior. 
(5.) Levator palpebrse superioris. 
(6) Rectus inferior. 
(7) Obliquus inferior. 
In 1881 Kahler and Pick (Prag. Zeitschrift f. Heilkunde , Bd. ii. 
p. 30), from the observations of two clinical cases of paralytic 
lesions of the muscles, were led to adopt a somewhat different, and 
what appears a priori to be a more natural arrangement. They 
placed the centres in a median and a lateral group, as follow : — 
(Read July 15, 1889.) 
Median Group. 
Tensor choroidese. 
Sphincter iridis. 
Rectus internus. 
Levator palpebrse superioris. 
Rectus superior. 
Obliquus inferior. 
Lateral Group. 
Rectus inferior. 
