THE STRUCTURE OF THE MEDULLA OBLONGATA 



137 



as they cross the median plane, the bundles from one side alternating with 

 similar bundles from the other, and largely obliterating the anterior median fis- 

 sure at this level. There is great individual variation as to the relative size of 

 the ventral and lateral corticospinal tracts; and there may even be marked 

 asymmetry due to a difference in the proportion of the decussating fibers on the 

 two sides. 



The nucleus gracilis and nucleus cuneatus (nucleus funiculi gracilis and 

 nucleus funiculi cuneati) are large masses of gray matter located in the pos- 

 terior funiculi of the caudal portion of the medulla oblongata. They are sur- 

 rounded by the fibers of these funiculi except on their ventral aspects, where they 

 are continuous with the remainder of the gray substance (Fig. 99). The fibers 



Funiculus gracilis 



Nucleus gracilis 



Spinal tract of trigeminal 

 nerve 



Nucleus of spinal tract of 

 N. V 



Central canal 



Decussation of the pyramids 

 Anterior column 



Posterior median fissure 

 Funiculus cuneatus 







Nucleus cuneatus 

 Dorsal spinocerebellar tract 

 Ventral spinocerebellar tract 

 Ventral fasciculus proprius 

 Bulbospinal tract 



Anterior median fissure 



Fig. 98. Section through the medulla oblongata of a child at the level of the decussation of the 

 pyramids. Pal-Weigert method. (X6.) 



of the gracile and cuneate fasciculi terminate in the corresponding nuclei; and 

 their terminal arborizations are synaptically related to the neurons, whose cell 

 bodies and dendrites are located there (Fig. 100). Accordingly, in sections 

 through successive levels we see the fibers decreasing in number as the nuclei 

 grow larger (Figs. 98, 99, 101). It is due to the presence of these nuclei that the 

 funiculi become swollen to form the club-shaped prominences with which we are 

 already familiar under the names clava and cuneate tubercle. At the level of the 

 pyramidal decussation the gracile nucleus has the form of a rather thin and 

 ill-defined plate, while the cuneate nucleus is represented by a slight projection 

 from the dorsal surface of the posterior gray column (Fig. 98). At the level of 

 the decussation of the lemniscus both have enlarged and the gracile nucleus has 

 become sharply outlined (Fig. 99). As the central canal opens out into the 



