CONSIDERATIONS OF THE BRAIN OR ENCEPHALON. 41 



well marked transverse groove containing the roots of the sixth, 

 the seventh, the intermediate and the eighth cerebral nerves. 

 The transverse strands of the pons traced lateralward are observed 

 to form a large round bundle, called the brachium pontis, which 

 extends into the hemisphere of the cerebellum on either side. Be- 

 tween those pontine strands, at the lateral border of the pons, 

 there should be noticed the roots of the great trigeminal nerve. 

 A sagittal line through this nerve at its attachment to the pons 

 may be regarded as the boundary between the pons and the cere- 

 bellar hemisphere. The hemispheres of the cerebellum form the 

 lateral part of the posterior area; their stratified appearance is 

 already familiar. Inferior to the pons is the medulla oblongata. 

 The medulla is about an inch long and three-quarters of an inch 

 broad near the pons, but measures less than one-half inch in 

 width at the lower end. It is partially divided into lateral halves 

 by the anterior median fissure, which is deep, above, but is almost 

 obliterated in the lower half of the medulla by the crossing of the 

 lateral pyramidal tracts, the decussatio pyramidum. On either 

 side of the anterior median fissure, the student should notice, in 

 this order, the pyramid, the olive, and the restiform body. The 

 pyramid (pyramis] bounds the anterior median fissure. It is 

 an eighth of an inch in width, is most prominent near the pons 

 and tapers off inferiorly because about 80 per cent, of its fibers 

 cross over to the opposite side and sink backward in the medulla. 

 It is bounded laterally by a slight longitudinal furrow, the anterior 

 lateral sulcus (sulcus lateralis anterior] which contains the roots 

 of the twelfth cerebral nerve, and separates the pyramid from the 

 olive and from a flat surface, called the lateral funiculus of the 

 medulla. The olive (oliva) occupies the upper half of the lateral 

 surface of the medulla; the lateral funiculus, the lower half. 

 The olive is equal in breadth to the pyramid. It is quite promi- 

 nent, is white in color and is elliptical in outline. The posterior 

 lateral sulcus (sulcus lateralis posterior) separates it from the 

 restiform body. The roots of the ninth, tenth and eleventh cere- 

 bral nerves, which are contained in that groove and the restiform 

 body which lies beyond it, can be seen only by pressing aside 

 the hemisphere of the cerebellum. 



