TRACTS THROUGH THE MEDULLA 



571 



ulus gracilis and funiculus cuneatus of either side, and they are looked upon 

 as a sensory decussation. 



The olivary bodies extend forward almost to the level of the pons. They 

 consist of both cells and fibers. The cellular matter consists of a plicated 

 thinnish layer of small nerve cells, folded upon itself in the form of a loop, 

 with the ends turned inward and slightly dorsal, figure 381, O. The gray 

 loop is filled with and covered by white fibers. 



Internal to the olivary body on either side are two small masses of gray 

 matter, one more ventral to the other, called accessory olives, external and 



't.C 



n.c' 



a.m.f. 



FIG. 380. Anterior or Dorsal Section of the Medulla Oblongata in the Region of 

 the Superior Pyramidal Decussation. a.m.f., Anterior median fissure; f,a., superficial 

 arciform fibers emerging from the fissure; py, pyramid; n.ar., nuclei of arciform fibers; /.a., 

 deep arciform becoming superficial; o, lower end of olivary nucleus; n.L, nucleus lateralis; 

 f.r., formatio reticularis;/.a. 2 , arciform fibers proceeding from the formatio reticularis; 

 g., substantia gelatinosa of Rolando; a.V., ascending root of fifth nerve; n.c., nucleus 

 cuneatus; n.c.', external cuneate nucleus; n.g., nucleus gracilis; f.g., funiculus gracilis; 

 p.m.f., posterior median fissure; c.c., central canal surrounded by gray matter, in which 

 are n.XI., nucleus of the spinal accessory, and n.XII., nucleus of the hypoglossai; s.d., 

 superior pyramidal decussation. (Modified from Schwalbe.) 



internal, and on the surface of the anterior pyramid on either side a small 

 mass of gray matter, external arcuate nucleus; laterally another mass of the 

 same material, the representative of the lateral nucleus of the cord, is seen, 

 viz., the antero-lateral nucleus, which gives origin to the spinal accessory 

 nerve. 



It will be necessary to follow as shortly as possible the fibers of the spinal 

 cord upward into the bulb and beyond. 



Tracts Through the Medulla. The crossed and direct pyramidal tracts 

 have already been described. Nothing definite is known of the antero-lateral 

 descending tracts. The direct cerebellar tracts pass laterally into the resti- 



