696 THE NERVOUS SYSTEM. 



cuneate tubercle, which is best marked in children. Above this point it disappears 

 from the surface. 



The funiculus gracilis is the direct continuation upward of the postero-median 

 column of the cord (tract of Goll). It is a narrow white band, placed parallel to 

 and along the side of the posterior median fissure. It is separated from the 

 funiculus cuneatus by a slight groove, continuous with that on the surface of the 

 cord, which marks off the postero-median column. At first the funiculi of the 

 two sides lie in close contact on either side of the posterior median fissure. Oppo- 

 site the apex of the fourth ventricle each presents an enlargement, the clava ; 

 they then diverge and form the lateral boundaries of the lower part of the fourth 

 ventricle, and gradually tapering off become no longer traceable. 



The Restiform Body. The upper part of the posterior area of the medulla is 

 occupied by the restiform body. It appears, at first sight, as if this body were the 

 direct continuation upward of the funiculus cuneatus arid the funiculus of Rolando, 

 and it was formerly described as such. This, however, is not so, for the restiform 

 body is largely formed by a set of fibres, the external arcuate fibres, which issue 

 from the anterior median fissure and will presently be described. They pass 

 laterally over the pyramid and olive, and assist in forming the restiform body. 

 There is also a narrow strand of fibres, derived from the lateral column of the 

 cord, the direct cerebellar tract, which joins the above-mentioned arcuate fibres. 

 These two sets of fibres, reinforced by the internal arcuate fibres from the opposite 

 side of the medulla, form the restiform body. 



The restiform bodies are the largest prominences of the medulla, and are 

 placed between the lateral tracts in front and the funiculus cuneatus behind, from 

 both of which they are separated by slight grooves. As they ascend they diverge 

 from each other, assist in forming the lower part of the lateral boundaries of the 

 fourth ventricle, and then enter the corresponding hemisphere of the cerebellum, 

 forming its inferior peduncles. 



The posterior surface of the medulla oblongata forms part of the floor of the 

 fourth ventricle. This portion is of a triangular form, bounded on each side by 

 the diverging funiculi graciles and cuneati and restiform bodies. The divergence 

 of these two funiculi and of the restiform bodies, together with the opening out 

 of the posterior fissure and central canal of the spinal cord, displays in the floor of 

 the ventricle the gray matter of the medulla, which is continuous below with the 

 gray matter of the cord. In the middle line is seen a longitudinal furrow, which 

 divides this part of the ventricle into right and left halves, and is continuous 

 below with the central canal of the cord. 



The arciform or arcuate fibres, which have been mentioned as forming part of 

 the restiform body, are found in the upper half of the medulla, crossing its surface 

 and also traversing its substance. They are divided for purposes of description 

 into two sets external and internal. The external or superficial arciform fibres 

 have already been alluded to as crossing the pyramid and olivary body on each 

 side. They emerge from the anterior median fissure, and if traced into it are 

 found to enter the raphe' and cross to the opposite side, after which their further 

 course is a matter of some doubt. After emerging from the anterior median 

 fissure they cross the pyramid and olivary body, often concealing from view the 

 upper part of the cuneate and Rolandic funiculi, and enter the restiform body. 

 As they cross the olivary body they are reinforced by some of the internal arciform 

 fibres, which come to the surface on the inner side of, or through, this structure. 

 The internal arciform fibres are described with the microscopic anatomy of the 

 medulla. 



It is advisable, at this stage, to take up the consideration of the cavity of the 

 fourth ventricle, an acquaintance with which will render the description of the 

 internal structure of the medulla oblongata more intelligible. 



