THE INCREASE IN THE NUMBER AND SIZE OF THE 

 MEDULLATED FIBERS IN THE OCULOMOTOR 

 NERVE OF THE WHITE RAT AND OF THE CAT 

 AT DIFFERENT AGES. 



THOMAS HARRIS BOUGHTON. 



{From the Neurological Laboratory of the University of Chicago.) 



With Three Figures. 

 INTRODUCTION. 



The present investigation is an attempt to determine the rate 

 of development and increase in the diameter of the medullated 

 fibers in a typical cerebral motor nerve of the white rat, and to 

 compare this development, on the one hand, with that of the spinal 

 motor roots of the same animal, and on the other, with the develop- 

 ment of the same nerve m an animal of a different species (cat). 



Schiller ('89) states that the oculomotor nerve of the cat is 

 practically complete at birth, and that the number of medullated 

 fibers increases only 3.2 per cent, between birth and eighteen 

 months. The number of fibers in the oculomotor nerve of the 

 cat according to Schiller's enumeration is as follows: 



New born (3 cases) 2942 



Eighteen months (i case) 303S 



This is quite at variance with what other investigators have 

 found as to the development of other motor nerves, ^. g., the spinal 

 motor roots in the frog and rat. Dr. Hatai ('03) working in this 

 laboratory, found that the number of medullated fibers in the 

 ventral roots of the spinal nerves in the w^hite rat increases about 

 170 per cent, in rats ranging in body- weight between 10.3 grams 

 and 264.3 grams, and that the increase is practically the same 

 in the cervical, thoracic and lumbar nerves. Birge ('82) counted 

 in the frog (R. esculenta), the medullated fibers in the roots of 

 all the spinal nerves on one side, and found an average increase 



