THE CENTRAL NERVOUS SYSTEM 



679 



grey and white matter of the spinal cord is rearranged, and, in 

 addition, new strands of fibres and new nuclei of grey substance make 

 their appearance. Of these nuclei the most conspicuous is the den- 

 tate nucleus of the inferior olive, which, covered by a crust of white fibres, 

 appears as a projection on the antero-lateral surface of the medulla. 

 In front of the olive, between it and the continuation of the anterior 

 median fissure, is another projection, the pyramid, which looks like 

 a prolongation of the anterior column of the cord, but is made up of 

 very different constituents. Dorsal to the olive is the restiform body 

 of inferior peduncle of the cerebellum, and behind the restiform body 

 lie two thin Columns, the funiculus cuneatus, which continues the 

 postero-external column of the cord, and the funiculus gracilis^ which 

 continues the postero-internal column. In these funiculi are con- 

 tained respectively the nucleus cuneatus and the nucleus gracilis. 

 The rearrangement 

 of the constituents 

 of the cord is due 

 mainly to two 

 causes : (i) The 

 opening up of the 

 central canal to form 

 he fourth ventricle, 

 and the folding out, 

 on either side, of the 

 grey matter which 

 lies posterior to it 

 in the cord; (2) the 

 breaking up of the 

 grey matter of the 

 anterior horn by 

 strands of fibres as 

 they sweep through 



it from the lateral FIG. 243. MEDULLA OBLONGATA AND CEREBELLUM, 

 WITH FOURTH VENTRICLE (HIRSCHFELD). . 



i, mesial groove of floor of ventricle running down to- the 



pyramidal tract to 

 take up a position 



in the pyramid of ca i amus scrTptorius ; 2, striae acusticae ; 3, inferior peduncle 

 the Opposite side of the cerebellum ; 4, clava ; 5, superior peduncle crossing 

 Mprii<;<;ation nf the the inferior and passing to its internal side ; 7, 7> lateral 

 , sulcus ; 8, corpora quadrigemina. 



pyramids), ana a > 



little higher up by fibres passing across the middle line from the 

 gracile and cuneate nuclei (sensory decussation or decussation of the 

 fillet). The mosaic of grey and white matter formed in the medulla 

 by the interlacing of longitudinal and transverse fibres with each other 

 and with the relics of the anterior horn, is called the reticular forma- 

 tion (formatio reticularis). It occupies the anterior and lateral portions 

 of the bulb behind the p>ramids and olivary bodies, and is con- 

 tinued upwards in the dorsal portion of the pons and crura cerebri. 



The cerebro-spinal axis passes up from the medulla through the 

 pons, encircled and traversed by the transverse pontine fibres derived 

 from the middle cerebellar peduncle or commissure, which enclose 



