632 PHYSIOLOGY. 



issuing from the column of Clarke. The root and commissural fibers 

 pass, without decussation, into the cuneate nucleus, or nucleus of 

 Burdach. 



Parts added to the medulla oblongata, which are not found in 

 the cord, are: arcuate fibers and olives. 



Arcuate fibers are the curved fibers which are seen in transverse 

 section of the medulla. By reason of their position they have been 

 termed superficial and deep, or external and internal 



The superficial arcuate fibers form a more or less voluminous 

 ribbon. They are fibers which come from the cells in Goll's and 

 Burdach^s nuclei. They proceed to the restiform body of the same 

 side and thence to the cerebellum. 



The internal arcuate fibers likewise proceed from the cells of the 

 nuclei of Goll and Burdach. The hindmost fibers form the sensory 

 decussation of the fillet. Other fibers cross the median raphe in 

 the substance of the medulla, then to pass upward into the brain. 



The olivary body is formed by a portion of the white cortical 

 substance which belongs to the lateral column, and by the corpus 

 dentatum, a layer of intervening gray matter folded upon itself, in 

 such a manner as to represent an oblong purse. This is open at its 

 internal aspect, and is known as the liilus of the olive. The corpus 

 dentatum of the olive is formed by a great quantity of small, multi- 

 polar cells. The fibers which emanate from it go to the olive of the 

 opposite side, traversing the raphe or mounting toward the pons. 



* 



Pons Varolii. 



The pons is a mass of nervous tissue placed transversely and in 

 the form of a half -ring. It is situated between the medulla oblon- 

 gata and cerebral peduncles, which limit it below and above, respec- 

 tively. The cerebellar hemispheres bound it laterally. Its. weight 

 is sixteen or seventeen grams. 



For examination microscopically the pons presents six surfaces 

 or faces. 



1. The anterior face is free, convex, and rounded, and rests upon 

 the basilar gutter of the occipital bone. It presents an antero-pos- 

 terior median depression: the basilar groove. On each side of this 

 are two parallel prominences due to the heaving up of the annular 

 fibers by reason of the anterior pyramids which pass through it. 



Upon this face are seen the transverse fibers which pass laterally 

 to penetrate into the corresponding hemisphere of the cerebellum. 



