180 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



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united and pass upward as the pyramidal column. The posterior 

 horns move more to the front, so as to occupy the space in the 

 lateral columns which was formerly filled by the pyramidal 

 tracts. 



The pyramidal decussation is fully completed a few milli- 

 metres above this point. Both the anterior direct and lateral 

 indirect pyramidal fibres are' united into a thick bundle on the 

 ventral side of the cord, which now bears the name of medulla 

 oblongata. This is clearly shown in Fig. 108. You see that 

 the ground-bundle (Fa'} of the anterior column has assumed a 

 position dorsad of the pyramids. External to the anterior horn, 

 which has been cut off from the rest of the gray matter by the 

 decussation of the pyramids, lies a small gray mass. It is the 

 commencement of the inferior olivary body. Higher up, the 

 olivary body increases greatly in size and occupies a large share 

 of the space once occupied by the lateral columns. These latter 

 have become somewhat less abundantly supplied with fibres since 

 the reticular process appeared on the scene. They still, how- 

 ever, send many fasciculi high up beyond the olivary body into 

 the reticular processes. On account of the continual distribution 

 of fibres to small gray nuclei situated in the latter, the supply of 

 these fibres soon becomes exhausted and the lateral columns can 

 be traced no farther. 



The two accompanying figures, taken from Henle, show 

 beautifully the general change in the arrangement of fibres and 

 the passage of the lateral columnar pyramidal tract to the oppo- 

 site anterior columns. The severed anterior horns can be traced 

 still farther upward, but are lost at about the level of the pons. 



You will see the pyramidal columns in the anterior part of 

 all following sections lying between the olivary bodies. (See the 

 figures of the next lecture.) At last they are covered in and 

 split up by the transverse fibres of the pons. We have learned 

 in previous lectures how they re-appear from under the pons, 

 and pass upward in the pedunculi to the internal capsule. We 

 have also seen that a break in the conductivity of the pyramid- 



