632 STRUCTURE OF THE BULB, PONS. & MID-BRAIN. [CH. XLIV. 



First section. This is taken at the lowest level of the bulb, 

 through the region of the decussation of the pyramids. The 

 similarity to the cervical cord will be at once recognised ; the 

 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 the anterior horn (A), which in sections 

 higher up appears as an isolated mass of grey matter, called the 

 lateral nucleus (fig. 467, id}. 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 

 Rolando (R), which causes a prominence on the surface called the 



Fig. 466. Section through the bulb at the level of the decussation of the pyramids, o. funi- 

 culus gracilis, continuation of column of Goll ; c, funiculus euneatus, continuation of 

 column 6f Burdach ; R, substantia gelatinosa of Rolando, continuation of posterior 

 horn of spinal cord ; L, continuation of lateral 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.) 



tubercle of Rolando ; G and C are the funiculi gracilis and cuneatus 

 respectively, the continuations upwards of the columns of Goll 

 and Burdach. 



Second section. 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 

 containing the nuclei of the eleventh and twelfth nerves; the funi- 

 culus gracilis (f.g.} comes next, and then the funiculus cuneatus 

 (/.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 



