THE NERVOUS SYSTEM. 591 



further and further toward the centre, while the lateral horn remains 

 near the lateral surface. The anterior gray matter becomes broken up 

 and merged into the reticular formation. There is also a similar reticu- 

 lar formation both toward the centre and also laterally in the dorsal 

 region. At the level where the central canal opens into the 4th ventri- 

 cle, the posterior pyramids diverging to form the lower and outside 

 boundaries, and inclosing a space, the calamus scriptorius, between 

 them, there are to be made out various masses of gray matter in addi- 

 tion to the reticular formation, viz., the nuclei of the fasciculus gracilis 



Fig. 361. Anterior or dorsal section of the medulla oblongata in the region of the superior 

 pyramidal decussation. a.m./., anterior median fissure; /.a., superficial arciform fibres 

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

 becoming superficial; o, lower end of olivary nucleus; n.l., nucleus lateralis; /.r., formatio 

 reticularis ; /. a. 2 , arciform fibres proceeding from the formatio reticularis ; g. , substantia ge- 

 latinosa 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./., posterior median fis- 

 sure ; c. c. , central canal surrounded by gray matter, in which are n. XL , nucleus of the spinal 

 accessory, and n.XIL, nucleus of the hypoglossal ; s.d., superior pyramidal decussation. 

 (Modified from Schwalbe.) 



and fasciculus cuneatus (361, n.g. and n. c.), which are at this level, 

 however, already diminishing and are lost at a level of the pons Varolii. 



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

 They consist of gray and white matter. The gray matter consists of a 

 plicated thinnish strand containing small nerve-cells, folded upon itself 

 in the form of a loop, with the ends turned inward and slightly dorsal 

 (Fig. 362, o). The gray loop is filled with and covered by white matter, 

 part of the fibres passing through the gray. 



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

 gray matter, one more ventral to the other, called accessory olives, ex- 

 ternal and internal, and on the surface of the anterior pyramid on either 



