542 



THE BRAIN 



neck of the posterior column, so as to reach the raphe. The caput 

 columme is in this way cut off from the basal portion. The basal portion 

 remains in close relation to the central canal, whilst the caput and 

 substantia gelatinosa (Rolando) is placed close to the surface, enlarges as it 

 is traced upwards, and forms the prominence on the surface which has been 

 described already as the funiculus and tubercle of Rolando. The fibres 

 which have thus broken up the neck of the posterior column, and which 

 come from the cuneate and gracile nuclei, are termed the internal arcuate 

 fibres. They reach the raphe on the deep or dorsal aspect of the pyramids, 

 and, in the median plane, they form a very complete decussation with the 

 corresponding fibres of the opposite side. This decussation is termed the 

 decussation of the lemniscus or the sensory deciissation. As soon as they 

 reach the opposite side of the medulla oblongata, the internal arcuate 



- Funiculus 

 gracilis 



Funiculus 

 cuneatus 



Tractus spinalis 

 of the trigemina! 

 nerve 



Cerebello-spinal 

 fasciculus 



Pyramid 



FIG. 229. Transverse section through the Medulla Oblongata of new-born 

 Child at the level of the lower part of the olive, stained by the Weigert- 

 Pal method. 



fibres turn upwards and form a longitudinal tract called the lemniscus. 

 It is placed close to the raphe and on the dorsal aspect of the corresponding 

 pyramid. 



The anterior column of grey matter shares a like fate in the medulla 

 oblongata, but at a lower level, at the hands of the fasciculus cerebro- 

 spinalis lateralis (O.T. crossed pyramidal tract). This great bundle, in 

 passing from the pyramid into the lateral funiculus of the opposite side of 

 the spinal medulla, traverses the anterior column, completely breaks up 

 its intermediate part and separates its head from its basal portion. The 

 further history of the detached head need not be traced, but it is well 

 to note that the basal part of the anterior column of grey matter remains 

 in position on the ventral and lateral aspect of the central canal. 



At a higher level the central canal, surrounded by the basal portions of 

 the two columns of grey matter, gradually inclines towards the dorsal aspect, 

 until it reaches the surface. The grey matter which surrounds it is now 

 spread out on the floor of the fourth ventricle, and in such a manner that 



