106 HAND-BOOK OF PHYSIOLOGY. 



of the spinal cord. Each half of the medulla, therefore, may be divided 

 into three columns or tracts of fibres, continuous with the three tracts of 

 which each half of the spinal cord is made up. The columns are more 

 prominent than those of the spinal cord, and separated from each other 

 by deeper grooves. The anterior, continuous with the anterior columns 

 of the cord, are called the anterior pyramids; the posterior, continuous 

 with the posterior columns of the cord, and comprising the funiculus cune- 

 atus, and the funiculus of Rolando (Fig. 323, /.c., /.#.), are called the 

 restiform bodies. On the outer side of the anterior pyramids of each 

 side,* near its upper part, is a small oval mass containing grey matter, 

 and named the olivary body; and at the posterior part of the restiform 

 column, immediately on each side of the posterior median groove, con- 

 tinuous with the posterior median column of the cord, a small tract is 

 marked off by a slight groove from the remainder of the restiform body, 

 and called the posterior pyramid or fasciculus gracilis. The restiform 

 columns, instead of remaining parallel with each other throughout the 

 whole length of the medulla oblongata, diverge near its upper part, and 

 by thus diverging, lay open, so to speak, a space called the fourth ven- 

 tricle, the floor of which is formed by the grey matter of the interior of 

 the medulla, by this divergence exposed. 



On separating the anterior pyramids, and looking into the groove 

 between them, some decussating fibres of the lateral columns of the cord 

 can be plainly seen. 



DISTRIBUTION OF THE FIBRES OF THE MEDULLA OBLOXGATA. 



The anterior pyramid of each side, although mainly composed of con- 

 tinuations of the fibres of the anterior columns of the spinal cord, receives 

 fibres from the lateral columns, both of its own and the opposite side; the 

 latter fibres forming almost entirely the decussating strands which are 

 seen in the groove between the anterior pyramids. Thus composed, the 

 anterior pyramidal fibres proceeding onward to the brain are distributed 

 in the following manner: 



1. The greater part pass on through the Pons to the Cerebrum. A 

 portion of the fibres, however, running apart from the others, joins some 

 fibres from the olivary body, and unites with them to form what is called 

 the olivary fasciculus or fillet. 2. A small tract of fibres proceeds to the 

 cerebellum. 



The lateral column of the cord on each side of the medulla, in pro- 

 ceeding upward, divides into three parts, outer, inner, and middle, which 

 are thus disposed of: 1. The outer fibres (direct cerebellar tract) go with 

 the restiform tract to the cerebellum. 2. The middle (crossed pyramidal 

 tract) decussate across the middle line with their fellows, and form a part 

 of the anterior pyramid of the opposite side. 3. The inner pass on to 

 the cerebrum, at first superficially but afterward beneath the olivary body 

 and the arcuate fibres, and then proceed along the floor of the fourth 

 ventricle, on each side, under the name of the fasciculus teres. 



