OF DENISON UNIVERSITY 



57 



J^ig. I,) the fibres of the twelfth enter on the ventral surface just lat- 

 eral to the pyramids, k, pass through the olivary body, which attains 

 its maximum development at this point, and then through the formatio 

 reticularis to its nucleus, b, on the floor of the fourth ventricle. The 

 cells of this nucleus are of the multipolar type, measuring from .05 to 

 .06 mm. in length, having nuclei about .01 mm. in diameter, with 

 nucleoli. The axis cylinder process generally passes into a bundle of 

 fibres leading to the root of the nerve. T^i,-". 5, Plate XV, presents a 

 magnified view of the entire nucleus as it appears at this jjoint. Just 

 laterad to this is situated the nucleus of the tenth nerve Plate XV, 

 Fig. I, a, and a magnified portion of the same Fig. 2, of the same 

 plate. The cells of this nucleus are somewhat smaller than those of 

 the twelfth, though of about the same number and form. Just laterad 

 to this nucleus is a large cluster of small cells which is evidently very 

 closely associated with it. 



Still laterad we find a large group of cells which may be divided 

 into two nuclei. • The lateral one, (Plate XV, Fig. t, r,) consti- 

 tuting xhQ cuncate nucleus, contains cells measuring about .03 mm., 

 imbedded in a very dense neuroglia (Plate XV, Fig. 6,) while the cells 

 of the median portion are very much smaller and are more numerous, 

 constituting the clavate nucleus. 



The formatio reticularis is very largely developed and rather abun- 

 dantly provided with cells which are of the multipolar type, measur- 

 ing about .04 mm. aud sending their processes in the general direc- 

 tions of the fibres in which they are imbedded. Plate XI\', Fig. 4, 

 will serve to illustrate their manner of distribution between the longi- 

 tudinal fasciculi of the reticular formation. 



There is a marked decussation of fibres in the lower i)<)rti()n of 

 the raphe in which are found multipolar cells of about .02-. 03 mm., 

 which here form a considerable nucleus, (Plate XV, Fig. i, <•, and a 

 magnified view of the same, Fig. 3, of the same plate.) The decus- 

 sation is of fibres from the olives, while large bundles api)ear to pass 

 through the olives and thus around into the irsfi/orm tracts. A small 

 lateral nucleus is also present. 



As we pass cephalad, in a section at the level of the ciuiin. «.- ..i 

 •the tenth nerve root, (Plate XVI, Fig. i,) we find the nucleus of the 

 twelfth nerve, r, still represented on the floor of the ventri<:le and the 

 nucleus of the tenth, b, very closely associated with it. The olives 

 are much reduced in size, the nucleus of the raphe in the decu.ssation 



