634 PHYSIOLOGY. 



Upon the median lino it has a groove which follows that of the 

 calamus scriptorius. Upon each side there exist two slight depres- 

 sions: the one known as the superior fovea, the other the locus 

 cocruleus. 



3. A superior face. 



4. The inferior face is continuous with the base of the medulla 

 oblongata. The annular fibers of the pons embrace as a half-circle 

 the anterior pyramids of the medulla oblongata. 



The two lateral faces (5 and 6) are mingled with the origin of 

 the middle cerebellar peduncles. The peduncles sink into the hemi- 

 spheres of the cerebellum, where they are lost. 



Structure of the Pons. The pons is composed of nerve-fibers 

 and scattered nerve-cells. It forms a kind of knot into which con- 

 verge the fibers coming from the cerebellum, as well as those passing 

 to and fro from the medulla into the cerebral peduncles. 



The transverse fibers which form the cortex of this organ go in 

 great part to the middle cerebellar peduncles. They are the com- 

 missural fibers which unite one cerebellar hemisphere to the other. 



Some fibers emanate from the middle cerebral peduncles and 

 decussate on the median line with those of the opposite side. They 

 thus form the median raphe. They terminate in the gray masses of 

 the pons. 



Other fibers, having decussated, bend upward and ascend into 

 the cerebral peduncles. All of the various fibers semi-annular, 

 horizontal, and oblique cover in the longitudinal fibers which unite 

 the medulla oblongata to the cerebral peduncles. In them various 

 planes are formed : (1) there is a superficial plane, or stratum zonale, 

 which covers the two pyramidal columns; (2) the stratum profundum, 

 which separates the pyramids from the fillet and upper part of the 

 pons; (3) the third plane, stratum complexium, separates the cerebral 

 tracts. It is this separation which gives rise to the formatio 

 reticularis of the pons and is continuous with 'the formatio reticu- 

 laris of the medulla. 



Between the superior, or pontal, olives there is a system of fibers 

 which envelops and covers the olivary nuclei to decussate upon the 

 median line back of the pyramids. It is to this system of fibers 

 which unite the nuclei of the auditory nerves and the olives that 

 Edinger has given the name of trapezoid body. 



The longitudinal fibers are in three groups: 1. The anterior 

 bundle, which contains the middle fibers of the cerebral peduncle, 

 and is continuous with the superficial motor fibers of the anterior' 



