CH. XLYI.] 



SECTIONS OF THE BULB 



667 



passage of the pyramidal fibres (P) from the anterior part of the 

 bulb to the crossed pyramidal tract of the opposite side of the cord 

 cuts off the tip of anterior horn (A), 

 which in sections higher up appears as 

 an isolated mass of grey matter, called 

 the lateral nucleus (fig. 411, nl). The 

 V formed by the two posterior horns 

 is opened out, and thus the grey 

 matter with the central canal is brought 

 nearer to the dorsal aspect of the bulb ; 

 the tip of the cornu swells out to 

 form the substantia gelatinosa of Ro- 

 lando (E), which causes a prominence 

 on the surface called the tubercle of 

 Rolando ; Gr and C are the funiculi 

 gracilis and cuneatus respectively, the 

 continuations upwards of the columns 

 of Goll and Burdach. 



Many of the fibres of the pyramidal tract 

 terminate in the mid-brain and pons, hence 

 this tract is reduced in size when it reaches 

 the bulb. The pyramidal fibres on their long 

 journey give off collaterals to the cortex 

 cerebri, the basal ganglia of the cerebrum, 

 the substantia nigra of the raid-brain, the 

 nuclei pontis of the pons, and lower down in 

 the cord to the base of its posterior horn. They, however, do not give off col- 

 laterals to the motor nuclei of the cranial nerves on their passage through the bulb 

 (Schafer). The only collaterals given off in this region are a few to the olivary nuclei. 



Second section (fig. 411). This is taken through the upper 

 part of the decussation. Beginning in the middle line at the top of 

 the diagram, we see first the posterior median fissure (p.m/.), below 

 which is the grey matter enclosing the central canal (c.c.), and con- 

 taining the nuclei of the eleventh and twelfth nerves ; the funiculus 

 gracilis (/.</.) comes next, and then the funiculus cuneatus (f.c.) ; these 

 two funiculi have now grey matter in their interior: these masses 

 of grey matter are called respectively nucleus gracilis (n.g.) and 

 nucleus cuneatus (n.c.) ; the fibres which have ascended the posterior 

 columns of the cord terminate by arborising around the cells of this 

 grey matter ; the fibres from the lower part of the body end in the 

 nucleus gracilis, and those from the upper part of the body in the 

 nucleus cuneatus. These nuclei form a most important position of 

 relay in the course of the afferent fibres from cord to brain. The 

 new fibres (the second relay of the sensory spinal path) arising from 

 the cells of these nuclei pass in a number of different directions, and 

 break up the rest of the grey matter into what is called iheformatio 

 reticularis (f.r.) 



FIG. 410. Section through the bulb at 

 the level of the decussation of the 

 pyramids. G, funiculus gracilis, con- 

 tinuation of column of Goll ; C, funiculus 

 cuneatus, continuation of column of 

 Burdach ; R, substantia gelatinosa of 

 Rolando, continuation of posterior horn 

 of spinal cord ; L, continuation of lat- 

 eral column'Of cord ; A, remains of part 

 of the anterior horn, separated from 

 the rest of the grey matter by the 

 pyramidal fibres P, which are crossing 

 from the pyramid of the medulla to the 

 posterior part of the lateral column of 

 the opposite side of the cord. 



(After L. Clarke.) 



