FUNCTIONS OF THE BRAIN.- 811 



medulla, this point of crossing being termed the decussation of the 

 pyramids (Fig. 351). 



The anterior pyramids are thus made up of the crossed pyramidal 

 tract from the lateral column of the opposite side of the cord, and the 

 direct pyramidal tract from the anterior column of the same side of the 

 cord. 



Of the pyramidal fibres some pass through the pons directly to the 

 cerebral cortex in a manner to be described directly, some pass to the 

 cerebellum, and some join fibres coming from the olivary body to form 

 the olivary fasciculus. 



The remainder of the anterior column, the antero-external fibres, lie 

 under the anterior pyramids and form part of the formatio reticularis. 



In the neighborhood of the first cervical nerve and the point of 

 origin of the first root of the hypoglossal nerve, laterally from the 

 anterior pyramids, lie the remainder of the lateral columns of the cord 

 winch have not undergone decussation, the direct cerebellar tract passing 

 backward to rejoin the restiform body and go to the cerebellum ; the 

 remaining fibres, passing underneath the olivary bodies and appearing 

 in the floor of the medulla, form the fasciculus teres and pass to the 

 cerebrum. 



Farther outward from the anterior pyramids are found the gray 

 masses of the olivary bodies, the pyramidal nucleus, and the accessory 

 olivary nucleus, through which passes toward the middle line and backward 

 the remainder of the anterior column. The gray substance of the olivary 

 bodies on section possesses the form of a horseshoe, whose arch is thrown 

 up into numerous folds and whose opening is directed toward the centre 

 of the medulla. It contains numerous small, yellow, pigmented multi- 

 polar ganglion cells, and embraces like a capsule a tract of medullated 

 nerve-fibres which enter through the hylus of the olivary bodies and 

 spread out over the entire inner surface of the gray substance. In all 

 probability some of these fibres terminate in the ganglion cells of the 

 olivary body. The remainder pass through the gray substance of the 

 olivary body and partly unite with the fibrous columns of the restiform 

 bodies and partly surround the exterior surface of the olivary bodies. 

 The gray substance of the pyramidal nucleus and the accessory olivary 

 nucleus resembles in all respects that of the olivary bodies. The former 

 lies in the hylus of the olivary bodies toward the posterior central line 

 of the pyramidal and olivary columns ; the latter, in the form of a thin, 

 concave plate of gray matter, lies between the olivary hylus and the 

 corpora restiformes, which, by a collection of gray matter (Clarke's 

 column), form an unbroken continuation of the posterior columns of the 

 cord to the cerebellum. 



The restiform bodies form the posterior division of the medulla 



