THE MEDULLA OBLONGATA. 



1067 



inferior cerebellar peduncle or restiform body. The expansion within the 

 upper part of the funiculus graciHs, the clava, contains the nucleus gracilis (nucleus 

 funiculi gracilis), the reception station in which the long sensory fibres of Goll's tract 

 are interrupted. The triangular interval included between the gracile funiculi, where 

 these begin to diverge, corresponds to the level at which the central canal of the cord 

 ends by opening out into the fourth ventricle. A thin lamina, the obex, closes this 

 interval and is continuous with the ventricular roof. 



Along the outer side of the gracile fasciculus and separated from it by the para- 

 median furrow, extends a second longitudinal tract, the funiculus cuneatus, which 

 at the lower end of the medulla receives the column of Burdach. Slightly above the 

 lower level of the clava, the cuneate strand also exhibits an expansion, the cunea'.e 

 tubercle (tuberculum cuneatumj, that is less circumscribed, but extends farther upward 

 than the median elevation. Beneath this prominence lies an elongated mass of gray 

 matter, the nucleus cuneatus (nucleus funiculi cuneati), around whose cells the long 

 sensory fibres of Burdach' s tract end. 



Still more laterally, between the roots of the ninth and tenth nerves and the 

 cuneate strand, the posterior area of the medulla presents a third longitudinal eleva- 

 tion, the funiculus of Rolando. The latter is caused by the increased bulk of the 



Fig. qiS. 



Inferior colliculus 



Cerebral peduncle 



Median fossa 



Median sulcus 



Middle cerebellar peduncle^ 



Acoustic striae 



Acoustic trigone 

 Restiform body 



Attachment of ventricular roof 

 Obex 



Funiculus cuneatus 



Frenulum 



Superior medullary velum 

 Cerebellar peduncle 



Floor of fourth ventricle 

 Fovea superior 



Eminentia teres 

 Trigonum hypoglossi 

 Trigonum vagi (fovea inferioi ) 



Funiculus sepatans 

 Area postrema 



Funiculus gracilis 

 Lateral area 



Medulla and floor ofiourth ventricle seen from behind, after removal of cerebellum and ventricular roof. X i}i. 



underlying substantia gelatinosa that caps the remains of the posterior horn of gray 

 matter, and is overlaid by a superficial sheet of white matter composed of the longi- 

 tudinal fibres of the descending root of the trigeminal nerve. While, therefore, the 

 tubercle of Rolando is produced by the exaggeration of gray matter represented 

 within the spinal cord, the gracile and cuneate nuclei are new stations in which the 

 posterior root-fibres not interrupted at lower levels end, and from which the sensory 

 impulses collected by the cord are distributed to the cerebellum and the higher 

 centres by neurones of the second order. 



The upper half of the posterior area of the medulla is modified by the presence 

 of the fourth ventricle, the lower lateral boundary of which it largely forms, into a 

 robust rope-like strand that diverges as it ascends. Above, it abuts against and fuses 

 with the lateral continuation of the pons and then, bending backward, enters the 

 overhanging cerebellum as the inferior cerebellar peduncle. This strand, also 

 known as the restiform body (corpus restiforme), is seemingly the direct prolongation 

 of the gracile and cuneate funiculi. Such, however, is not the case, since the fibres 

 passing from these tracts to the cerebellum by way of the restiform body are the axones 

 of the gracile and cuneate nuclei and, therefore, new links in the chain of conduction. 



