MEDULLA OBLONGATA 479 



glosso-pharyngeal posteriorly. It presents a very different 

 appearance in its upper and lower parts. In its lower 

 portion it appears to the eye as a continuation upwards 

 of the lateral funiculus of the spinal medulla ; in its upper 

 part the striking oval prominence, named the olive, is seen. 



The lower part of the district, however, is very far from 

 being an exact counterpart of the lateral funiculus of the spinal 

 medulla. It has been noted already that the large fasciculus 

 cerebrospinalis lateralis, which in the spinal medulla lies 

 in the lateral funiculus, is not present in that district of the 

 medulla oblongata; above the decussation of the pyramids 

 it forms the chief part of the pyramid of the opposite side. 

 Another small strand of fibres, the dorsal spino-cerebellar 

 fasciculus (O.T. direct cerebellar tract), prolonged upwards in 

 the lateral funiculus of the spinal medulla, gradually leaves 

 the lateral portion of the medulla oblongata. The tract of 

 fibres in question lies on the surface, and it is often visible 

 to the naked eye as a white streak inclining obliquely into 

 the posterior district of the medulla oblongata to join its 

 upper part, which is called the restiform body. The great 

 majority of the remainder of the fibres which are prolonged 

 upwards from the lateral funiculus of the spinal medulla dis- 

 appear from the surface at the lower border of the olive, by 

 dipping into, the substance of the medulla oblongata under 

 cover of that projection. A narrow band, however, passes 

 upwards to the pons, in the interval between the posterior 

 border of the olive and the fila of the vagus and glosso- 

 pharyngeal nerves. 



The olive is a smooth, oval prominence, which occupies 

 the upper part of the lateral area of the medulla oblongata. 

 Its long axis, which is vertical, is about 12.5 mm. (half an 

 inch) long, and its upper end is separated from the lower 

 border of the pons by an interval or groove. 



Posterior Area of the Medulla Oblongata. The constituent 

 parts of the lower half of the posterior region are the cuneate 

 and gracile funiculi ; in its upper half they are the ependymal 

 roof of the fourth ventricle, medially, and the diverging funi- 

 culi, laterally. 1 It is separated from the lateral area on each 



1 The dissector should note that the lower part of the cavity of the hind- 

 brain, i.e. the fourth ventricle, is not behind but in the upper part of the 

 medulla, which it separates into dorsal and ventral parts ; the dorsal part forms 

 a portion of the roof of the ventricle, whilst the ventral part forms a portion of 

 the floor. 



