CORPUS PYRAMID ALE. 571 



corpus pyramldale. All the constituent fibres of the motorial 

 part of the cord, do not share in the decussation. Those on the 

 front and on the back part of the column, making about two- 

 thirds of the whole, cross in bands one over another, like the 

 fingers of the two hands when obliquely interlocked, while 

 the middle fibres of each motorial tract, pass straight up 

 through the pons to the hemisphere of the brain of the same 

 side.* 



On tearing carefully the corpus pyramidale from above 

 downwards in a prepared organ, or separating it in the manner 

 of Cruvielhier by the aid of a jet of water, it will be found that 

 some of the decussating fibres are in contact with the gray 

 substance, and that the inner face of the pyramid, has a column 

 of gray neurine attached to it, which increases in bulk as it 

 approaches the pons, and near which it terminates abruptly ; 

 this is considered as representing in position, a portion of the 

 anterior horn of the nucleus of the cord. 



The white fibres of the exterior, dip round the gray matter 

 at its abrupt termination near the pons, and thus form the groove 

 between the medulla oblongata and the pons, which is filled up 

 with a process of the pia mater. 

 On the outer side of the pyramid is placed the 



Corpus Olivare. 



This is a body of a ganglionic shape, formed interiorly of 

 a vesicle of cineritious neurine arranged in folds, which, accord- 

 ing to Burdach, is appended to the anterior horn of the gray 

 substance belonging to the cord. Hence this vesicle is filled 

 in its centre with white fibres, as well as covered on its outer 

 surface with the white fibres which belong to the exterior of the 

 medulla oblongata. 



* The fact of the decussation of these fibres, which is now universally ad- 

 mitted, was first pointed out by Mistichelli in 1709. A decussalion of the fibres 

 had been believed to exist somewhere ; as early as the time of Hippocrates and 

 Aretseus, in consequence of injuries of one side of the head, producing very 

 generally, palsy of the opposite side of the body. All the fibres not crossing, 

 we are enabled to comprehend, why palsy is sometimes, though very rarely 

 found to occur on the same side of the body with the cerebral lesion. 



