BouGHTON, Oculomotor Nerve. l6i 



the life of the animal, but the newer fibers, classed as "small," 

 and first recognized at fifteen days, never attain the size of the 

 older ones, and, indeed, at two years of age they are not so large 

 as some of the older fibers were at fifteen days. This appears 

 to be due to the fact that they come in after the period of most 

 rapid growth. 



5. At any age at which the two groups of " large " and " small" 

 fibers can be distinguished, all the fibers are increasing in diameter 

 at the same rate. 



6. At any age, the area of the sheath in the fully medullated 

 fiber is nearly equal to the area of the axone. 



PART II. THE CAT. 



In this part of the investigation, the oculomotor nerves from 

 six cats (a mother and her five kittens) were used. There were 

 three males and three females, ranging in weight from 112 grams 

 (one day) to 2893 grams (thirteen years). The technical methods 

 used were the same as in the case of the rats {q. v.) and the con- 

 clusions drawn were almost identical. 



An inspection of the tables and figures brings out the following 

 points: 



I. There is a nearly regular increase in the number of medul- 

 lated fibers in the oculomotor nerves of cats increasing in body- 

 weight from 112 grams (one day) to 2804 grams (six months). 

 In the case of the 2893 gram cat (thirteen years old) there is a 

 falling oflp in the number of fibers, due, probably, to senile changes. 

 The single irregularity in the curve (the cat of 223 grams body- 

 weight) is probably not significant, being merely an individual 

 variation. The increase between the limits here given (one day 

 to six months) amounts to 157 per cent. (The increase in the case 

 of the rats, between much wider limits, was only 75 per cent.) The 

 medullation in the cat at one day is about as far advanced as that 

 in the cat at ten days, so that a direct comparison between the 

 two series just as they stand is not misleading. The oculomotor 

 nerve in the cat, then, develops more rapidly during life than that 

 of the rat, and this may be related to the greater functional impor- 

 tance of the eye in the cat. It will be noticed that the number of 

 fibers in Schiller's cases (about 3000) corresponds roughly with 

 the number of "large" fibers which I obtained, although still 



