632 



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



FIG. 461. Section through the bulb at 

 the level of the decussation of the 



o, funiculus 



tinuation of column of Goll ; 

 cuneatus, continuation of column of 

 Burdach; B, substantia gelatinosa of 

 Rolando, continuation of posterior horn 

 of spinal cord ; L, continuation of lat- 

 eral column of cord ; A, remains of part 



parts more evident. The position of our seven sections is indicated 

 by the transverse lines numbered 1 to 7. 



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 pyra- 

 midal 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. 462, 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 (K), which causes a prominence 

 on the surface called the tubercle of 

 Rolando; G- and C are the funiculi 

 posterior part"ortiw"ia^rc(Jumn^f gracilis and cuneatus respectively, the 

 fth ( e Af?e r r d L. ciarke.) 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 mid-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 collaterals 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. 462). 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.ra/.), 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 (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 body end in the 

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



