MORPHOLOGY OF EYE MUSCLE NERVES 63 



primary protoplasmic path connecting its nidulus and its end- 

 organ — that in this respect the histogenesis of the oculomotor 

 resembles that of a spinal somatic motor nerve as described 

 above. The evidence about to be presented goes to show that 

 the midbrain vesicle becomes connected with the first head- 

 cavity by means of the movement or continuous extension of 

 the protoplasm of neuroblasts situated in the somatic motor 

 column of the midbrain. 



There is, however, a slight difference in the conditions under 

 which connection of tube and somite are effected as compared 

 with those which obtain in the growth of spinal somatic motor 

 nerves. As a result of the late appearance of the oculomotor 

 anlage, relatively to the formation of a loose mesenchyma in 

 the head, the region between midbrain and somite, which had 

 been earlier filled with an unstaining plasmoid substance, becomes 

 filled with a loose mesenchyma of uncertain origin, and proto- 

 plasmic connection of tube and somite is effected by growth in 

 the midst of loose mesenchyma. Since it is almost as difficult 

 to find the oculomotor anlage in the midst of this connective 

 tissue, especially in preparations made by the older non-neuro- 

 logical methods, as to find the proverbial needle in a haystack, 

 it is not surprising that the discovery of the true manner of 

 growth of the nerve has been delayed and that difference of 

 opinion has arisen. 



Since, however, today all investigators, whose observations are 

 sufficiently extended to cover this point, agree that midbrain 

 and the first head cavity become connected with each other 

 secondarily, and since the opposite view is, for this nerve, an 

 assumption without a single drawing or demonstration to sup- 

 port it, there seems to be no good reason why an affirmative 

 answer should not be given to the question: Are protoplasmic 

 connections between somite 1 and midbrain primary or second- 

 ary? Held's ('09) assertion, that the neurofibrillae of the oculo- 

 motor alw^ays appear as intra-plasmatic fibrils, affords no founda- 

 tion for inductions regarding the genesis of these protoplasmic 

 paths. Held himself admits that he does not know whether the 

 paths are primary or secondary. 



