COUESE OF FIBRES. 509 



c, central canal and grey substance surrounding it ; /, anterior median fissure ; fp^ 

 posterior median fissure; r, and rn, restiform body and nucleus; p pi, and p p 11, 

 posterior pyramid and its nucleus ; t r, tubercle of Rolando ; I, lateral column ; the 

 anterior column of the cord is indicated by p in A, its remains by a c in B ; jj in the 

 other figures indicates the anterior pyramid ; in B, its decussation ; a in B points to the 

 remains of the anterior cornu ; in E to the superficial arciform fibres : I, latei'al column ; 

 o, olivary body; 0', the commissural fibres proceeding from its interior ; R, raphe; C, 1, a, 

 and Gl p, anterior and posterior roots of first cervical nerves ; viii' (E and F), inner audi- 

 tory nucleus ; X, pneumogastric nerve ; x' ( x in F), its nucleus ; xi, 'spinal accessory nerve ; 

 xi', its nucleus ; xii, hji^oglossal nerve ; xii', its nucleus (which should extend nearer 

 to the middle line than is represented in E). 



Course of fibres from the spinal cord upwards through the 

 medulla oblongata. — Assuming, for convenience of description, the 

 existence of three white cokimns of the cord, these are disposed as follows. 



1. T\\Q posterior colinnn, with the exception of the posterior median 

 column (from which it is here distinguished as the processus cuneatus), 

 enters into the formation of the restiform body, which ascends to the 

 cerebellum. The posterior median column (posterior pyramid or fasci- 

 culus gracilis) ascends to the cerebrum. 



2. The lateral columii ascends towards the base of the olivary body, 

 and is disposed of in three ways ; (1,) some of its fibres from the sur- 

 face and deep part join the restiform body and proceed with it to the 

 cerebellmu; (2,) a large number pass obliquely inwards, then come 

 forwards between the anterior columns, and, crossing the median plane, 

 appear as the fibres of decussation, and form the chief part of the 

 opposite anterior i^yramid; (3,) the remaining fibres pass up to the 

 cerebrum, as the fasciculus teres, appearing on the back of the pons 

 Varolii, in the upper part of the floor of the fourth ventricle. 



3. The anterior cohinms (fig. 356, a, a') having reached the apex of 

 the anterior pyramids, are thrust aside fi'om their median position by 

 the decussating fibres derived from the lateral columns, and are then 

 distributed in three divisions. (1,) A very small division, ascends ob- 

 liquely backwards beneath the olivary body, and joins the restiform body 

 (Solly) (fig. 356, r). (2,) Another division passes directly upwards, and 

 its fibres embrace the olivary nucleus, above which they are again 

 collected together, and are joined by other fibres arising from the 

 nucleus, so as to form the oJivarij fasciculus (fig. 356, 0'); this ascends 

 through the pons and at the side of the cerebral peduncle under the 

 name of the ^//ef (fig. 363, /), and reaches the corpora quadrigemina 

 and the cerebral hemispheres. (3,) The remaining division of the 

 anterior column ascends into the anterior pp-amid, forming its outer 

 part. The anterior i\yramids therefore are composed of fibres from the 

 lateral column and grey substance of the opposite side, and from the 

 anterior column of the same side, and are continued up through the 

 pons into the peduncles of the cerebrum. 



It is to be remembered, however, that the separation between these 

 different tracts of white fibres cannot be clearly followed out through 

 the whole structure of the medulla oblongata, but that they are more 

 or less blended with one another. 



Grey matter of medulla oblongata followed upwards from the 

 cord.— At the level of the first cervical nerve (fig. 357, A, 348, C, 1), the 

 central grey substance is increased in size, the posterior horn on each side 

 is thrown outwards, its neck is slender and its extremity (caput cornu) is 



