372 SPECIAL HISTOLOGY. 



the nerves into the substance could not escape notice. Since the junction 

 of the radical fibres with the anterior, posterior, and lateral columns, 

 can be so well and so directly observed, the relation in question would 

 necessarily be evident also ; and yet in the course of my perfectly unpre- 

 judiced observations, I have never seen anything of the kind. Nothing, 

 therefore, remains but to assume, that the great majority of the periphe- 

 ral nerves really have a cerebral origin. Whether they all originate in 

 the brain (where, we shall afterwards see) or in part, though, from my 

 observations, but to a small extent, from the cord, cannot be determined, 

 any more than the question can be decided, whether the white substance 

 of the cord, besides the fibres derived from the peripheral nerves, also 

 contains others passing from the brain to the cord. 



114. The medulla ollongata and pons Varolii belong to the most 

 complex parts of the central nervous system, containing white and gray 

 substance, intermixed in very various modes. The tvhite substance is, in 

 part, a continuation of that of the cord, in part distinct from it, and is 

 disposed in the following manner : the anterior columns of the spinal 

 cord diverge from each other at the commencement of the medulla oblon- 

 gata, allowing the decussating fibres of the corpora pyramidalia to 

 appear. As they proceed, a smaller division joins the pyramids, form- 

 ing their outer part, whilst the principal portion surrounding the olivary 

 bodies, internally and externally, whence they are also termed the oli- 

 vary columns, passes laterally, and then, divided into two bundles, 

 proceeds above the second transverse layer of fibres, through the pons. 

 One of these divisions constitutes the fillet (laqueus), which continued 

 above the crura cerebelli ad cerebrum, enters the posterior corpora quad- 

 rigemina, joining, within them, the corresponding division of the opposite 

 side. The second division, or bundle, lies externally and inferiorly to 

 the crura cerebelli, and enters the tegmentum of the cerebral peduncle. 

 Besides this, the olivary columns, corresponding to the anterior columns 

 of the cord, also, as it seems, give off fibres to the pedunculis cerebelli. 

 The lateral columns of the spinal cord divide, on reaching the medulla 

 oblongata, into three bundles ; one of which, ascending in a tolerably 

 straight direction, is continuous with the fasciculus lateralis of the resti- 

 form body, and with it enters for the most part into the peduncle of the 

 cerebellum, and in small part into the tegmentum ; a second division 

 penetrates forwards between the divergent anterior columns, decussates 

 in two or three fasciculi with that of the other side (decussatio pyrami- 

 durii), constituting the principal bulk of the pyramids ; a third division, 

 lastly, appears between the posterior columns at the bottom of the 

 rhomboid fossa, or fourth ventricle, as the eminentia teres. These latter 

 are continued, on the floor of the fourth ventricle and applied to each 

 other, into the tegmentum of the cerebral peduncles, whilst the pyra- 



