264 THE RIG IX OF VERTEBRATES 



As far as the anatomist is concerned, the evidence is becoming 

 clearer and clearer that the nucleus of the Illrd 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, Obersteiner, Edinger, Kolliker, 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 lar^e 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 Kolliker 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 

 bis 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, i.e. 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, 



