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



various parts of the cerebrum, but the sensory impulses go through 

 one or more cell-stations (positions of relay) before they ultimately 

 arrive at the cortex. We now see that the brain has a crossed 

 relationship to the body, the left half of the brain governing the 

 right half of the body, and vice versd, both as regards motion and 

 sensation ; the motor fibres mostly cross at the decussation of the 

 pyramids, some few (those in the direct pyramidal tract) crossing at 

 lower levels in the cord; the sensory fibres mostly cross at the 

 decussation of the fillet, though some few cross at lower levels in the 



n.am 



n. ar. 



FIG. 4(33. Section of the medulla oblongata at about the middle of the olivary body, f.l.a., anterior 

 median fissure; n.ar., nucleus arcuatus; p, pyramid; XII. , bundle of hypoglossal nerve emerging 

 from the surface; at 6, it is seen coursing between the pyramid and the olivary nucleus, o; f.a.e., 

 external arcuate fibres ; n.L, nucleus lateralis ; a., arcuate fibres passing towards restiform body, 

 partly through the substantia gelatinosa, g., partly superficial to the descending root of the fifth 

 nerve, d. V. ; X., bundle of vagus root emerging; f.r., formatio reticularis; C.r., corpus restiforme, 

 beginning to be formed, chiefly by arcuate fibres, superficial and deep ; n.c., nucleus cuneatus ; n.g,, 

 nucleus gracilis ; t, attachment of the ligula; f.s., funiculus solitarius ; n.X., n.X.', two parts of 

 the vagus nucleus; n.XIL, hypoglossal nucleus; n.t., nucleus of the funiculus teres; n.am., 

 nucleus ambiguus; r., raphe; A., continuation of the anterior column of cord; o', o", accessory 

 olivary nucleus; p.o.L, pedunculus olivse. (Modified from Schwalbe.) 



cord, soon after their entrance into the cord by the posterior nerve- 

 roots. 



Other points to be noticed in the section are the substantia 

 gelatinosa of Eolando (g) (remains of posterior cornu of the cord), 

 now separated from the surface by the descending root of the fifth 

 nerve (d. V.) ; the lateral nucleus (n 1) (remains of the anterior cornu 

 of the cord) ; the lower part of the grey matter of the olivary body 

 (o, o'), and most anteriorly the pyramid (py). 



Third section. This (fig. 463) is taken at about the middle of 

 the olivary body, and passes also through the lower part of the floor 



