56 GRAY SUBSTANCE OF THE TRAPEZIUM, 



thick stem, which may be traced like the nerve roots to the outer limits of the 

 mecIuUa (Plate XVI, Fig. 12^ y). 



Schroder van der Kolk^ has deduced from the connections between the upper 

 olivary body and the nucleus from which the facial arises, the theory that the upper 

 olivary body is a sort of accessory nucleus to the facial, establishing the same relation 

 between them which he supposes to be established between the hypoglossal and the 

 lower olivary body. A connection between these nuclei undoubtedly exists to some 

 extent in those mammalia which I have examined, but the chief and by far the most 

 important connection of the olivaries, both upper and lower, is with the arciform 

 fibres, and I am therefore inclined to think that the upper olivary bodies, like the 

 lower, are co-ordinating centres for the different nuclei lying in the same region 

 with them, with all of which they are brought into more or less intimate relation 

 by means of the plexus of arciform as well as transverse fibres with which they are 

 connected. Within the human pons Varolii a collection of cells is found near the 

 facial, undoubtedly representing the upper olivary body of the mammalia, but in 

 man, the ofiice of co-ordination would seem to be chiefly fulfilled by the numerous 

 scattered cell-groups, which are so frequently found in the meshes of the intricate 

 plexus of fibres constituting the pons Varolii. 



Several other cell groups are found, both on the outer and inner side of the upper 

 olivary bodies, and very many cells are found scattered throughout the whole 

 anterior and antero-lateral network. Among these groups, the largest and most 

 constant are, one on the inner side of the olivary body in the vicinity of the roots 

 of the sixth nerve, consisting of stellate, multipolar cells of moderate size, and 

 another on the outer side of the olivary body, near the entrance of the facial roots 

 (Figs. 10% 12", v), consisting of quite large multipolar cells, and sometimes, as 

 noticed by Schroder van der Kolk, forming two distinct groups, the cells of which 

 become more and more numerous, and at the same time are pushed inwards as we 

 reach the upper part of the course of the facial, continuing to increase both in size 

 and number as we approach the fifth nerve, to the motor root of which, I suspect, 

 this group is related as AveU as to the facial. 



METHODS OF PREPARATION. 



Among all the different and numerous methods of preparing specimens of the 

 medulla for microscopic examination, I have found none at all comparable to the 

 methods given by Clarke (PJiilos. Trans. 1859), and I have therefore availed myself 

 exclusively of these, with some slight modifications. Specimens colored by a solution 

 of carmine in glycerine^ have often been used for special purposes ; but for the general 

 study of the course and destination of fibres, I have found specimens hardened in 

 chromic acid and made transparent by Clarke's method, particularly well suited. 

 These specimens have usually been immers'ed for a few weeks in a solution of 

 chromic acid, of about the strength given by Clarke (1859), and subsequently put 



' Medulla Oblongata, 165. » Mem. of the American Academy, 1861. 



