718 THE NERVOUS SYSTEM. 



which will be mentioned below. Each restiform body passes into the cerebellum 

 (see under " dorsal surface " of the medulla), and is therefore known, also, as the 

 inferior peduncle of the cerebellum. 



The white fibres of the deep portion, or formatio reticularis, will now be 

 described. 



Fibres of formatio reticularis in both closed and open portions of the medulla. 

 These fibres are described as longitudinal, transverse, and dorso-ventral. The 

 longitudinal fibres really make up the bulk of the deep portion (ail three " areas ") 

 of the medulla. Most of them come directly from the antero-lateral ground bundle 

 of the cord, while others are derived from cells in the gray matter of the formatio 

 reticularis itself. They are all more or less directly continued upward into the pons, 

 and thence into the mid-brain and inter-brain. All of them have by no means 

 been traced definitely from origin to destination. This last statement is equally 

 true of the transverse and dorso-ventral fibres. But there are certain bundles in 

 all these fibres which have been quite clearly made out, and these will at once be 

 described. 



Longitudinal Fibres of the Formatio Reticularis. In each anterior area, just 

 dorsal to the pyramid, is seen on section a well-marked bundle of fibres. This is 

 the fillet, or lemniscus. Traced downward, each fillet, at about the level of the 

 lower end of the pyramid, bends dorsally and mesially, and then most of its fibres 

 decussate across the middle line (raphe) with the corresponding fibres of the oppo- 

 site fillet, and proceed to the cuneate and gracilis nuclei of the opposite side, in 

 the cells of which they terminate. This decussation of the fillet is dorsal to and 

 above the decussation of the pyramids. The remaining fibres of each fillet are 

 traceable downward on the same side to (1) the lateral tract of the medulla, 

 and thence to the antero-lateral ground bundle of the cord ; (2) a few fibres run 

 through the trapezium of the pons to the ventral auditory nucleus of the opposite 

 side. 



The Posterior Longitudinal Bundle. This is a band of fibres running upward 

 in each anterior area dorsal to the fillet. Below, its fibres are continued directly 

 into the "lateral tract," and thence into the antero-lateral ground bundle of the 

 cord. Both this and the fillet are continued upward into the pons and mid-brain, 

 where their final distribution will be described. 



In the lateral area the longitudinal fibres do not appear in any well-marked 

 bundles. Those on each side of and in front of the olive have been described. 

 Those dorsal are merely indeterminate fibres of the formatio reticularis or belong 

 to the internal arciform fibres (see page 719). 



In the posterior area, besides the indeterminate fibres, two rather distinct 

 bundles are to be noted. One is ihefuniculus solitarius, and the other the ascend- 

 ing root of the fifth nerve. 



The Ascending Boot of the Fifth Nerve. This is seen on section (Fig. 417) 

 to lie just external to the gray matter of the tubercle of Rolando and dorsal to 

 the issuing root-bundles of the vagus. Lower down, its fibres may take origin 

 from the cells of the tubercle of Rolando, but this is considered doubtful. 

 Passing upward, this root enters the pons, and contributes most of the fibres of 

 the regular sensory root of the fifth nerve (see page 722). 



The Funiculus Solitarius. This lies just ventral to the principal nuclei of the 

 vagus and glossopharyngeal nerves. It is round on section, and is surrounded 

 by g ra j matter. Traced downward, this bundle gradually disappears ; upward, 

 its fibres join with the roots of origin of the ninth and tenth, especially the 

 former. It may thus be regarded somewhat as an " ascending root " of these 

 nerves. 



Transverse and Dorso-ventral Fibres. The transverse fibres are found chiefly 

 in the formatio reticularis of the upper half of the medulla. Of these the most 

 important or, rather, those which have been more or less definitely traced are 

 known as external and internal arciform fibres. 



The external arciform fibres have already been described on the surface of the 



