HUMAN AND MAMMALIAN. 37 



Various authors have attempted to trace the course of the fibres within the 

 olivary bodies, and their relations to the cells of the lamina, but with little success, 

 v/ith the single exception of the very complete and accurate description given by 

 Clarke.^ The subject is an exceedingly difficult one, but after studying a large 

 number of preparations, both colored and uncolored, in which the course of the 

 fibres was as clear as possible, I am satisfied of the entire accuracy of Clarke's 

 description in all particulars. The only point remaining was to ascertain whether 

 the structure was the same in longitudinal as in transverse sections. 



Fig. 39, Plate XI, represents one of the folds of the lamina as seen in a longitu- 

 dinal section (Fig. 30), in which the arrangement of cells and fibres is strikingly the 

 same as that represented by Clarke (Philos. Trans. 1858, Plate xv, Fig. 25) in 

 connection Avith which it will be weU to study it. From the longitudinal bundles 

 which proceed upwards in the vicinity of the raph^ (Fig. 30), forming the very 

 beautiful network seen in transverse sections (Fig. 29), numerous bundles turn off 

 at varying angles, especially in the lower part of the medulla, radiating towards tht; 

 convolutions of the lamina. The course of one such bundle as it enters the fold is 

 seen in Fig. 39, Plate XI. The main bundle (A) enters the convolution just as 

 Clarke has described and figured the course of similar bundles in transverse sections. 

 (1st.) The inner fibres constituting the axis of the bundle proceed directly inwards 

 to the apex of the fold, where they spread out more or less towards the cells of the 

 lamina, with the processes of which many of them are continuous, while 

 others radiate and pass among the cells in the most varied directions. These fibres 

 sometimes cross over the lamina and pursue an onward course towards more distant 

 convolutions, or pass stiU further forwards to the anterior portion of the meduUa, 

 nearly parallel to the surface of which a folded portion of the lamina is disposed 

 (Fig. 30). The fibres passing through the lamina pursue a transverse course for a 

 very short distance, but soon turn upwards or downwards, joining the longitudinal 

 marginal fibres which run along the anterior surface of the medulla, forming quite a 

 thick band in connection with the arciform fibres with which they are interwoven. 



(2d.) The external fibres of the bundles are very divergent, some of them termi- 

 nate in cells lying near their course, but by far the greater number traverse the 

 lamina either singly or in biuidles ; the latter are sometimes very conspicuous ( C, C), 

 partly crossing over and partly joining the next lying bundle, entering the neighbor- 

 ing lamina in a course opposite to the one we have been considering. Some of the 

 cells belonging to the next fold of the lamina are represented at (D), the lamina 

 folding around the bundle (B) at each extremity, just about where the letters (B, 

 B) stand, so that the bundle (B, B) which constitutes the outer bundle to one fold 

 of the lamina, becomes in its turn the inner bundle of the next two, such bundles 

 as ((7, G, C) uniting them, or, as is frequently the case, passing stiU further 

 onwards to more distant folds of the lamina. These bundles follow so varied courses, 

 and cross and interlace in so many directions, that any description, however careful, 

 must of necessity be exceedingly indefinite. 



It is evident that fibres from all the different nuclei of the medulla pass among 



> Philos. Transactions, 1858, 244. » 



