734 



DISSECTION OF THE BKAIN. 



How to 



expose the 

 pyramidal 

 fibres. 



taking hold of a bundle of fibres in the forceps or fingers and gently! 

 tearing them up that they will separate in their proper direction. 

 To expose the connection of the pyramid with the spinal cord! 

 he should take hold of with the forceps and turn outwards on 

 the left side, as in fig. 263, the small part of the anterior column | 

 of the cord at the lowest part of the specimen (which will be below 

 the decussation), and the pyramid of the right side will then be seen! 

 to divide below into two parts, one passing directly into the anterior 

 column, and the other crossing the median fissure and disappearing 

 in the opposite half of the cord. Similarly an incision about |th 



FIG. 2b'3. SUPERFICIAL DISSECTION OF THE MEDULLA OBLONGATA AND PONS. 



a. Anterior pyramid. 



b. Decussation of the pyramids. 



c. Pyramidal fibres in the pons. 



d. The same in the crus cerebri. 



c. Superficial fibres of the pons, 

 cut through and reflected. 



/. Superficial fibres of the pons, in 

 place. 



Fibres of 

 the pyramid 



direct, 



of an inch deep will be made in the middle line of the pons and its 

 superficial fibres stripped transversely and the pyramidal fibres 

 carefully cleaned upwards on the right side, when they will be found 

 to pass into the lowest part (crusta) of the crus cerebri. 



Pyramid and anterior column. The fibres of the pyramid form 

 well-defined and independent bundle (seen in section on fig. 265 a, 

 p. 736) through the whole extent of the medulla oblongata, and are 

 continued below partly into the anterior column of the same side 

 of the cord and partly into the lateral column of the opposite half. 

 The set of fibres keeping to the same side forms the outer portion of 

 the pyramid, but in the anterior column of the cord, where it is- 

 known as the direct pyramidal tract, it is placed close to the anterior 



