600 THE BRAIN. 



pursue a course which is at first ventral along the side of the anterior fissure ; 

 and then lateral over the ventral surface of the pyramid and olivary nucleus, 

 by which path they reach the lateral surface of the bulb, and so the restiform 

 body and cerebellum. In this way the two nuclei in question contribute to 

 the restiform body of the opposite side of the bulb. These external arcuate 

 fibres, which as they sweep round the ventral surface of the pyramid traverse 

 the arcuate nucleus, though they vary much in individual brains, form a 

 considerable portion of the white matter seen on the ventral and lateral sur- 

 faces of the bulb ; it is by them that the olivary nucleus is covered up. 



The cuneate and gracile nuclei, besides this crossed and somewhat round- 

 about connection with the restiform body of the opposite side, are believed 

 to have more direct connection with the restiform body of the same side by 

 means of fibres which pass by a more or less direct lateral path from them to 

 it. Accepting this view, we may say that the two nuclei are connected with 

 the opposite side of the cerebellum by external arcuate fibres, and with the 

 same side of the cerebellum by the other fibres just mentioned. In any case, 

 the connection between the two nuclei and the cerebellum is large and im- 

 portant. 



Thus the important strand of fibres which is called in the bulb the resti- 

 form body, and higher up the inferior peduncle of the cerebellum, is con- 

 nected with the spinal cord in two chief ways ; directly by means of the 

 cerebellar tract and indirectly by means of the cuneate and gracile nuclei, 

 which, as we have said, diminish in bulk forward as the restiform body 

 increases. By the relay of the gracile nucleus it is brought into connection 

 with the median posterior column along the whole length of the cord, and so 

 with that division of the posterior roots which ( 490) in each of the several 

 spinal nerves goes to form that column. By the relay of the cuneate nucleus 

 it is brought into connection with such parts of the external posterior column 

 as end in that nucleus, and thus probably with other fibres of the posterior 

 roots of the upper spinal nerves. And if we admit that the cerebellar tract 

 is connected, by the relay of the vesicular cylinder or by other nerve-cells, 

 with the rest of the posterior roots of the spinal nerves, we may conclude 

 that the restiform body is, by means of these relays, a continuation of the 

 spinal posterior roots. 



The restiform body and so the cerebellum is also specially connected with 

 the olivary body of the opposite side ; for when in young animals one side 

 of the cerebellum is removed, the olivary body of the opposite side atrophies. 

 The course of the fibres maintaining this connection is not as yet accurately 

 known, but they probably pass from the olivary nucleus of one side through 

 the inter-olivary layer, and so laterally through the reticular formation of 

 the other side. Lastly, we may add that a tract which is sometimes included 

 in the restiform body as its median or inner division has quite a different 

 origin from any of the above ; the fibres which compose it come, as we shall 

 see, from the auditory nerve. 



The further connections of the bulb with the cerebrum it will be best to 

 leave until we come to deal with the structural arrangement of the rest of 

 the brain. 



Meanwhile enough has been said to show that the bulb differs very mate- 

 rially in structure from the spinal cord. The gray matter of the bulb is far 

 more complex in its nature than is that of any part of the cord ; and the 

 arrangement of the several strands and tracts of fibres is far more intricate. 

 The structural features on the whole perhaps suggest that the main functions 

 of the bulb are twofold : on the one hand, it seems fitted to serve as a head- 

 centre governing the spinal cord, the various reins of which, with the ex- 

 ceptions noted, it holds, as it were, in its hands ; on the other hand, it ap- 



