200 KENJI NITTONO 



up to 100 days, and finally the period of the very slow growth 

 follows and continues up to 485 grams in body weight. 



The percentage of water in the skeleton shows also a close 

 agreement with the growth phases of the ganglion cells and the 

 fibers. 



From these resemblances in the manner of maturation of 

 these various characters — teeth, cranium, and gasserian ganglion 

 cells and fibers — the following brief statement may be made. 



From eight to ten days after birth the incisors of the upper 

 and lower jaws erupt and shortly after that (about twelve days) 

 the myelination of the nerve fibers becomes evident. From 

 twenty to twenty-three days of age the molars in both the upper 

 and lower jaws erupt, the incisors are already well elongated 

 and the rat is able to maintain an independent existence. 



Before weaning the gnawing apparatus must be adequate, and 

 indeed we notice that the cranium is well developed not only 

 in size and weight, but, as is indicated by the loss of water, the 

 solidity of the cranium becomes adequate to give firm support 

 to the teeth and to resist the strain produced during the gnawing. 

 For an adequate supply of the nerves to these organs, the cell 

 body increases in volume very rapidly, and at the weaning time 

 the cell body and the nucleus have already reached the appear- 

 ance which they have in the adult rat. The nerve fibers also 

 approximate in area those found in the adult. At about thirty- 

 five days of age the third molars erupt in both the upper and 

 lower jaws and at the same time the ganglion cells have become 

 considerably larger, and at puberty or earlier, all the organs above 

 described show full development. 



COMPARISON OF THE MEASUREMENTS ON THE NEURONS OF THE 



FIFTH CRANIAL NERVE WITH THOSE MADE ON THE 



SEVENTH CERVICAL SPINAL NERVE BY 



DONALDSON AND NAGASAKA (18) 



It was one purpose of the present study to determine whether 

 the size and growth of the neurons in the gasserian ganglion 

 was like that found in a typical spinal nerve or, if not, to indicate 

 the differences observed. As both sets of specimens were pre- 

 pared by the same technical methods, the values may be directly 

 compared. 



