THE BRAIN AND ITS MEMBRANES. 



713 



between the pyramid and olive, those of the last-named group between the olive 

 and restiform body. It is thus seen that these fibres, traced dorsally, are right 

 in line with the corresponding groove, ventro-lateral and dorso-lateral, and the 

 similarity between the methods of division of the 4> deep portion " of the medulla 

 and its surface" is rendered complete; thus, the root-bundles of the twelfth 

 separate the anterior and lateral areas, while those of the seventh (some of the 

 eighth), ninth, tenth, and eleventh, according to the level, run between the lateral 

 and posterior areas. 



Each of the above "areas " is made up of gray and white matter, the former 

 being derived in part from that of the cord. The latter is composed of fibres, 



yucleus offuniculus teres. 



yucleus anting. 



Raphe- 

 Formatio reticuiaris 



Vagus nuclei. Ligula. 

 Hypoglossal 



niculus Soil/arms. 

 Xucleus gracilis. 



Continuation of antero-.- 

 lateral ground-bundle 



.Accessory olivary nuclei -f- 



'ucleus citneahts. 



Corpus restiforme. 



Nucleus of Rolando 



'Ascending root of 

 fifth, nerve. 



'agus root. 



Arciform fibres. 

 ^Nucleus lateralis. 



ivary nucleus. 



Hypoglossal nerve, 

 cleus of ext. arc. fibres, 

 ternal arciform fibres. 

 Anterior median fissure. 



FIG 417. Section of the medulla oblongata at about the middle of the olivary body. (Schwalbe.) 



some longitudinal, directly continued up from the cord, and others running for 

 the most part transversely, but with a slight dorso-ventral curve, and intersecting 

 the preceding ones. Between these intersecting fibres are scattered the various 

 cells and nuclei of gray matter which, together with their processes, form a net- 

 work. This network, together with the intersection of the white fibres, gives a 

 reticular appearance to cross-sections of the medulla, which is known as the 

 for/r>a f >" rt'ti'.'iilaris. 



As there is quite a difference between the structure and appearance of both 

 af'-'is and fn/i<itio reticuiaris as they occur in the upper (ventricular) or lower 

 (closed) portion of the medulla, as well as between that of the corresponding sur- 



*. it will be more convenient to describe the internal structure of each half 

 of the medulla separately. 



THE LOWER OR CLOSED PART OF THE MEDULLA. The gray matter is here 

 more directly continuous with that of the cord, the central canal of which is still 

 present, but placed dorsally, and the posterior median fissure and decussation of 

 the pyramids are also seen. The '"widening-out " of the medulla and the decus- 

 sation of the crossed pyramidal tracts of the cord are the prime factors in bring- 

 ing about the following changes in arrangement of the gray matter as compared 

 to that of the cord (see Figs. 418, 419, and 420). The anterior cornu (in the 

 cord) is broken up by the crossed pyramidal tract passing through it from behind 

 forward and inward to gain the pyramid of the opposite side. The caput cornu 



