184 



DISSECTION OF THE BRAIN. 



an inch long. A shallow groove separates it from the pyramid, and a 

 deeper and wider one intervenes between it and the restifbrm body. This 

 eminence is shorter than the pyramid, and does not reach to the pons. 

 Its upper end is most prominent ; and arching round the lower end, and 

 over the surface, are some white fibres (fibrin arcifbrmes). 



Restiform body ( 3 ). The restiform body (restis, a rope) forms the 

 largest prominence on the half of the medulla oblongata, and cannot be 

 seen satisfactorily except on a distinct preparation. It is posterior to the 

 lateral tract, and projects on the side, so as to give the width to the upper 

 part of the medulla oblongata. Behind, the restiform bodies diverge above 

 from each other, and between them is the space of the fourth ventricle. 



The posterior pyramid (funic. gracilis) (fig. 55, 4 ) lies along the side of 

 the posterior median fissure, and is much narrower than either of the other 

 component pieces. By drawing forwards the medulla it will be seen to 

 be slightly enlarged (clava) at the apex of the fourth ventricle, and then 

 to become gradually indistinct along the inner part of the corpus restiforme. 



STRUCTURE. From the interposition of the medulla oblongata between 

 the brain and the spinal cord, it is continuous with both. Below, the con- 

 stituent pieces of the half join directly (as before said) those of the spinal 

 cord ; but, above, they are continued chiefly to the cerebrum, only one 

 piece (restiform) entering the cerebellum. 



Dissection (fig. 56). The student has now to show the continuity of the 

 constructing parts of one-half of the medulla oblongata with those of the 



Fig. 56. 



a. Anterior pyramid. 



b. Decussation of the medulla oblon- 



gata (decussation of the pyra- 

 mids). 



c. Fibresof the pyramid in the pons. 



d. Fibres of the pyramids in the crus 



cerebri. 



e. Superficial fibres of the pons, cut 



through and reflected. 

 /. Superficial fibres of the pons, in 

 place. 



FIBRES OF THE MEDULLA, PONS AND CRCS CEREBRI. 



spinal cord. Let him trace out first the fibres of the pyramid on the right 

 H<1- : in it two sets of fibres have to be shown one from the same, and 

 one from the opposite side of the cord. The fibres from the opposite half 

 of the cord will appear in the median fissure, when the pyramids are gently 

 drawn from one another, where they are named the decussating fibres ; 

 and to lay these bare more completely, the small part of the anterior 



